Geology of the Manchester district—a brief explanation of the geological map, sheet 85 Manchester

R G Crofts, E Hough, A J Humpage and H J Reeves

Bibliographic reference: Crofts, R G, Hough, E, Humpage, A J, And Reeves, H J. 2012. Geology of the Manchester district — a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50 000 Sheet 85 Manchester (England and Wales).

Keyworth, Nottingham: British Geological Survey, 2012.

Printed in the UK for the British Geological Survey by B&B Press Ltd, Rotherham.

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(Front cover) Castlefield in central Manchester. The Chester Pebble Beds Formation (Sherwood Sandstone Group) are exposed along the Bridgewater Canal, with the Beetham Tower, built in 2007, a striking representative of redevelopment in the region (Photographer: P Witney; P770101).

(Rear cover)

Notes

'District' is used in this Sheet Explanation to denote the area included in the geological 1:50 000 Series Sheet 85 Manchester. National Grid references are given in square brackets throughout this explanation. All lie within the 100 km squares SD and SJ, and are prefixed accordingly. Borehole records referred to in the text are prefixed by the code of the National Grid 10 km2 sheet upon which the site falls, for example, SD80NW. Photographs are from the BGS archive, registration numbers are given in captions.

Acknowledgements

The series editors are M A Woods and J E Thomas. Figures were drawn by J Smalley and page setting was by A J Hill.

The National Grid and other Ordnance Surveydata ©Crown Copyright and database rights 2012. Ordnance Survey Licence No. 100021290.

We acknowledge assistance provided by the Coal Authority, Environment Agency, Urban Vision (Greater Manchester Geological Unit) and numerous civil engineering consultants. Landowners, tenants and quarry owners are thanked for permitting access to their land.

Geology of the Manchester district (summary from rear cover)

(Rear cover)

An explanation of sheet 85 (England and Wales) 1:50 000 series map—summary

The geology of Manchester, described in this Sheet Explanation, is one of the principal factors that underpinned economic growth in the region during the 1800s. The large-scale industrialisation that took place needed a supply of natural resources, including coal, brick clay, limestone and ironstone, many of which were sourced locally. The expansion of the city and surrounding towns was facilitated by the construction of rail and canal networks, which included the Bridgewater Canal, the first of the industrial age built in 1763 to transport coal. The Liverpool and Manchester Railway, the world's first intercity passenger railway, was built across the challenging ground conditions of Chat Moss peat bog under the guidance of George Stephenson in 1829. A contraction in traditional industries saw deep coal mining cease in the 1970s; currently there is limited mineral extraction, including coal and sand and gravel, with groundwater extracted for use in engineering processes and brewing.

The oldest bedrock exposed in the district is the Millstone Grit Group (upper Carboniferous), which comprises a sequence of interbedded sandstones, siltstones and mudstones and subordinate thin beds of coal that were deposited in large river deltas that flowed from the north. Overlying these are in excess of 2000 m of the Pennine Coal Measures Group deposited in shallow swamps across which short-lived rivers flowed.

By early Permian times, desert conditions prevailed, depositing thick dune sandstones of the Appleby Group. The Cumbrian Coast Group comprises mudstone with a marine influence; this is overlain by a thick sequence of mixed fluvial–aeolian sandstone of the Sherwood Sandstone Group.

A typically thin cover of superficial deposits mantles much of the district, dating from the late Devensian glaciation. These deposits thicken to over 80 m in numerous sediment-filled channels cut in the bedrock. Glacial material has been reworked during the Holocene as river terraces and alluvium. Peat has accumulated in several lowland areas, most notably Chat and Ashton mosses. Landslide development has occurred along the steeper slopes of some of the deeply incised streams and rivers.

Chapter 1 Introduction

This Sheet Explanation provides a summary of the geology and applied geology of the district covered by the geological 1:50 000 Series Sheet 85 Manchester, published as bedrock, and superficial and simplified bedrock editions in 2010 and 2011 respectively. Further details of the geology may be found in the references listed in the Information sources section and in other literature cited in the text.

The Manchester district lies almost entirely within the Metropolitan County of Greater Manchester, with the extreme south-western part being in Cheshire. The area supports a population of over two million people, concentrated in the cities of Manchester and Salford, and the surrounding towns of Ashton-under-Lyne, Oldham, Bury, Bolton, Trafford, and parts of Rochdale and Stockport. Between these areas, the land is used for a diverse range of activities, including agriculture and industry; there are also extensive tracts of public open space and amenity areas.

High ground of the Rossendale Plateau lies to the north of the district, with the Pennines along the eastern margin. These upland areas are drained by rivers including the Croal, Irwell, Irk and Medlock, which converge in the district. Many of the rivers flow southwards or westwards, through the largely featureless northern part of the Cheshire Plain. Completed during the 1890s, the Manchester Ship Canal was cut along the Irwell valley downstream of Salford Quays, allowing direct access by cargo ships to the city from the Irish Sea.

The bedrock is composed of rocks deposited during Carboniferous, Permian and Triassic times, up to about 220 million years ago (Figure 1). The Craven Group comprises up to 750 m of dark grey mudstones which are known from borehole and seismic data to lie conformably on Visean (lower Carboniferous) limestones of the Holme High Group. These are succeeded by Namurian rocks, represented by the Millstone Grit Group, a thick succession of interbedded sandstone, siltstone and mudstone, along with subordinate thin coals and seatearths. The Millstone Grit Group crops out on the eastern edge of the area. Commonly it forms upland scenery with extensive moorland associated with poor, acid soils. The thick sandstone units form a series of dissected escarpments with thin peat cover. Locally, this area provides catchments for water to be supplied to the main urban centres of the district. The sandstones have been extensively exploited as a building stone.

The Millstone Grit Group is overlain by the Pennine Coal Measures Group of Langsettian (Westphalian A) to Asturian (Westphalian D) age, a succession of mudstone, siltstone and sandstone with subordinate beds of coal, seatearth and ironstone that is over 2000 m thick. These form part of the sedimentary fill to the south Lancashire Coalfield. A fault-bounded inlier, the Bradford Coalfield, is present in east Manchester. The strata of late Bolsovian and Asturian age within the Warwickshire Group (Etruria and Halesowen formations) are principally primarily reddened, but are also secondarily reddened beneath the Permian unconformity. The Pennine Coal Measures Group crops out extensively in the northern and eastern part of the district. About 800 m of a dominantly sandstone sequence overlies the Carboniferous rocks, comprising the Appleby, Cumbrian Coast and Sherwood Sandstone groups, which form rockhead in the southern part of the district.

Unconsolidated Quaternary deposits dating from the late Devensian glaciation overlie bedrock across almost the entire district. A thin veneer of these deposits occurs on the higher ground but forms a thick, almost continuous cover on the lower ground in the south and west of the district. In addition, prior to, or during the early Devensian, narrow channels were carved into the bedrock by glacial meltwater. During the subsequent Holocene, there has been significant landsliding within the area, prompted by stream rejuvenation in valleys and because of glacial over-deepening of valleys in the east of the district. Glacial material has also been reworked as river terrace deposits and alluvium, and extensive shallow lakes became vegetated leading to peat moss and mire development.

The River Irwell allowed access from the Irish Sea and the Romans established the first permanent settlement in Manchester (Mamucium). The abundant water supply from rivers and groundwater helped stimulate rapid urban expansion in the 18th and 19th centuries. With access to abundant mineral resources of coal and sandstone, as well as brick clay from Carboniferous rocks and Quaternary deposits, Manchester became one of the power houses of Victorian industrialisation with the focus on cotton goods. The industrial development fuelled the demand for coal; the Bridgwater Canal was the first of the industrial age, built to transport coal from mines at Worsley to Manchester, and by 1854 there were approximately 100 active collieries in the district (Hunt, 1855). By the early 2000s, there was only limited mineral extraction in the district, although substantial volumes of groundwater were still being pumped from the Permo-Triassic sandstone aquifer.

History of research

The district covered by Sheet 85 Manchester was originally surveyed on the six inches to the mile scale and published as 1:63 360 'Old Series' sheets 88NW and 89NE between 1862 and 1874. The primary survey account of the geology is given by Hull and Slater (1862) and Hull (1864). The district was resurveyed at 1:10 560 scale in 1924–27 and Sheet 85 was published at 1:63 360 scale as Solid and Drift editions in 1930. The solid edition was partially revised and published at 1:50 00 scale in 1975. The accompanying memoir (Tonks et al., 1931) provided a detailed account of the geology of the district with descriptions of localities and regional variations. The present resurvey was carried out on the 1:10 000 scale by R G Crofts, E Hough, S J Price, A J Humpage, R A Ellison and R S Lawley between 2001 and 2005.

Recent advances in Carboniferous geology have necessitated some amendments to the previous surveys. Following the work of Ramsbottom et al. (1978), various publications have addressed regional and local aspects of the cyclicity (Holdsworth and Collinson, 1988), sedimentology (Collinson and Banks, 1975; Broadhurst and Simpson, 1983; Bristow, 1988; Collinson, 1988; Guion and Fielding, 1988; Guion et al., 1995; Chisholm et al., 1996; Waters, et al., 1996; Brettle, 2001) and palaeontology (Trueman and Weir, 1946; Calver, 1968; Eagar et al., 1985) of the Namurian and Westphalian. Kirby et al. (2000) provided insights into the regional structural history of the Carboniferous.

Other than during the geological surveys, the Quaternary deposits have been little studied during the last 150 years. Works of note include Binney (1848), Jowett (1914), March (1918), Johnson (1969), Worsley (1967), Johnson (1985), Crofts (2005a; and references therein), and Bridge et al. (2010).

Chapter 2 Geological description

Regional setting and structure

In earliest Carboniferous times a major rift-basin system developed across northern England in response to regional backarc extension, caused by northward subduction of the Rheic Ocean. Extension was much diminished in Namurian and Westphalian times and a regional 'post-rift' or 'sag' basin developed (Leeder, 1982). In latest Carboniferous times (about 300 million years ago), final closure of the Rheic Ocean caused large-scale thrust and nappe emplacement in central Europe and southern Britain. This period of tectonic activity is known as the Variscan Orogeny. On the foreland to the north of the fold belt, deformation was much less pervasive, so that in northern England tectonic disturbance was largely restricted to basin inversion, with partial reversal of the same earlier Carboniferous basin-controlling normal faults, associated folding and regional uplift.

The district lies on the northern margin of the Cheshire Basin, with the eastern edge of the district lying along the western limb of the north-trending Pennine Monocline (Figure 2). Over much of the district, strata dip mainly to the south or south-east with a dip of 5 to 15° common. By contrast, in the east dips increase to 30° on the western limb of the Pennine Monocline. The structure of the Pennine Monocline has been described in detail by Evans et al. (2002) who interpreted the fold to represent a positive inversion structure developed over a north–south basement fault, reactivated and subjected to oblique slip during north-west directed Variscan compression. Evans et al. (2002) suggested the Pennine Anticline developed above a complex zone of high-angle reverse faults with throws down to the west, which connect to an east-dipping, low-angle reverse fault with downthrow to the west and termed the Central Pennine Reverse Fault.

In the Manchester district, the early Carboniferous extensional basin system is concealed by Namurian and Westphalian post-rift strata. Interpretation of seismic reflection data shows a mosaic of tilt blocks bounded by large, east-north-east-trending syn-rift normal faults, with throws commonly of several hundred metres. The depth to Caledonian basement is less than 3000 m on fault-bounded horsts such as the Heywood High (Figure 2). These positive syn-rift structures are characterised by relatively thin Tournaisian to Visean successions (about 800 to 1200 m thick). Carbonate platforms developed around and over the Heywood High (Evans and Kirby, 1999). Thicker more basinal sequences, more than 2000 m thick, occur in the Rossendale Basin, thinning to less than 1200 m south of the Heywood High. Biostatigraphical correlation with the more extensive Tournaisian to Visean carbonate platforms of the Askrigg Block has proved largely unsuccessful (Riley and McNestry, 1988).

The post-rift Namurian and Westphalian successions are generally of more uniform thickness than the underlying strata, although the lower part of the Namurian succession shows a significant thinning to the south. The thinning probably relates to the basinward thinning and fining of late Namurian deltaic deposits overlying a relatively deep basin fill deposited during early Namurian times. The post-rift strata are dominated by north-north-west faults, as mapped at surface. Some of these may have been active as early Carboniferous transfer faults, whilst others may have a late Carboniferous or younger origin.

Carboniferous

Visean

Visean rocks were proved in the Heywood No. 1 oil exploration borehole (SD80NW/141), drilled in 1984 between Heywood and Birch [SD 83851 08976]. This encountered the Heywood High, a structural high on the footwall of the Rossendale Basin half-graben (Figure 2). The strata comprise 158 m of brown limestone with veins of calcite and pyrite, interbedded with grey and dark grey mudstone, assigned to the upper part of the Holme High Limestone Group (Waters et al., 2009), of Brigantian age (Figure 3). The top of the group is sharply conformable, taken at the base of overlying dark grey, carbonaceous, fissile mudstone of the Bowland Shale Formation.

Namurian

Namurian rocks crop out on the eastern fringe of the district, and within inliers at Three Lane Ends [SD 835 092], Harwood Fields [SD 828 128], Limefield [SD 810 131], and Horrock Fold [SD 708 132]. However, these rocks also occur at depth elsewhere underlying Westphalian and Permo-Triassic rocks beneath the district. The succession comprises a dominantly argillaceous basal unit, the upper part of the Craven Group, conformably overlain by the Millstone Grit Group, a thick succession of interbedded mudstone and siltstone (generally poorly exposed) and sandstone chronostratigraphical unit, the Millstone Grit Series (Wright et al., 1927), which included all strata of Namurian age, including the dominantly argillaceous strata now included with the Craven Group. It has been estimated that only the uppermost 395 m of the Millstone Grit Group occur at outcrop, with seismic reflection data suggesting that the total thickness of Namurian strata ranges from about 1800 m in the north-west decreasing to about 1150 m towards the south-east of the district. The Heywood No. 1 Borehole proved 77 m of the Bowland Shale Formation (Craven Group) and an almost complete sequence through the Millstone Grit up to the middle part of the Rossendale Formation (Figure 3).

During Namurian times, approximately 320 Ma, northern England lay within a large, actively subsiding basin, the Pennine Basin. Extensive delta systems built out into the basin, supplied with sediment derived from the land surface to the north, but also from the west by early Yeadonian times. Variations in sea level are reflected in the Millstone Grit Group by distinct cycles of sedimentation, each beginning at a high sea-level stand with the deposition of marine mudstone, including fossiliferous marine bands that are typically a few centimetres thick. They can be recognised regionally, and as each marine band generally contains a distinctive and diagnostic marine ammonoid (goniatite) assemblage, they are important marker horizons. About 50 marine bands are recognised in the Millstone Grit Group of the Pennines (Holdsworth and Collinson, 1988). The marine bands commonly pass up from mudstone into siltstone and sandstone representing a transition from sedimentation on the delta slope to deposition within distributary channels on the delta top. During late Namurian times, the top of each cycle (when sea level was at its lowest) was commonly marked by the formation of soils and the development of widespread vegetation, which when lithified became seatearths and coal respectively.

The Bowland Shale Formation (Brigantian– Pendleian) is known from the Heywood No. 1 Borehole. Here the formation comprises dark grey, fissile, calcareous mudstone, with interpretations of seismic reflection data indicating that the unit thickens to about 350 m in the southern part of the district.

The Millstone Grit Group (MG) comprises six formations (Waters et al., 2009); in ascending order these are: Pendleton, Silsden, Samlesbury, Hebden, Marsden and Rossendale formations (Figure 1). Only the uppermost two are exposed in the district, but the rest are proved by the Heywood No. 1 Borehole. The base of the group is taken at the top of the Cravenoceras malhamense (E1c1) Marine Band.

The Pendleton Formation, of Pendleian age, includes the Pendle Grit and the Warley Wise Grit. The former is a coarse-grained feldspathic sandstone interbedded with subordinate silty mudstone and siltstone interpreted as turbidite facies that were deposited on a prodelta slope. The base of the formation is defined as the base of the lowest turbiditic coarse-grained sandstone present above the Bowland Shale Formation. The Warley Wise Grit is a cross-bedded and cross-stratified medium-grained sandstone with sporadic pebbles and some siltstone interbeds. The top of the formation is identified by the base of the Cravenoceras cowlingense Marine Band, which is not known at outcrop in the district but is known from the Garstang area to the north (Aitkenhead et al., 1992). The formation is about 95 m thick in the Heywood No. 1 Borehole, with interpretations of seismic reflection data indicating up to 400 m may be present beneath some parts of the district.

The Arnsbergian Silsden Formation comprises dark grey mudstone with marine fossils, and paler mudstone, siltstone and very rare sandstones. The formation is variable in thickness, with about 200 m proved in the Heywood No. 1 Borehole, and seismic reflection data indicating only 80 m elsewhere.

The Samlesbury Formation is Chokierian to Alportian in age and comprises grey mudstone and siltstone. The top of the formation is taken at the base of the Hodsonites prereticulatus (H2c2) Marine Band, at the base of the overlying Hebden Formation. The Salmesbury Formation is about 30 m thick in the Heywood No. 1 Borehole.

The Hebden Formation is Kinderscoutian in age and includes the Todmorden Grit and the lower and upper units of the Kinderscout Grit. The Todmorden Grit is a feldspathic, coarse-grained sandstone interbedded with subordinate silty mudstone and siltstone, deposited on a prodelta slope and interpreted as of turbiditic facies, whereas the Kinderscout Grit was deposited on the delta top. The top of the formation is defined by the base of the Bilinguites gracilis (R2a1) Marine Band. The formation is about 515 m thick in the district.

The Marsdenian Marsden Formation (Mar) comprises mudstone and siltstone with some delta-top sandstones. Many of these sandstones show similar petrographical and sedimentological features and can only be distinguished one from another by their position relative to known marine bands. The sandstone nomenclature used herein is broadly similar to that used in the previous survey but with the rationalisation to a single name for the Gorpley Grit and Fletcher Bank Grit to the Fletcher Bank Grit (FB). In addition, the Brooksbottoms Grit is now known to be coeval with the Huddersfield White Rock (Waters et al., 2009), and the Holcombe Brook Grit (HB) is later in age. The top of the formation is defined by the base of the Cancelloceras cancellatum (G1a1) Marine Band. The formation is about 350 m thick in the Heywood No. 1 Borehole, but varies from 300 to 600 m across the district.

The uppermost unit, the Rossendale Formation (Ros) is Yeadonian in age and comprises mudstone and siltstone with several finger-bar sandstones represented by the Lower and Upper Haslingden Flags (Collinson and Banks, 1975). These sandstones have a distinctive westerly provenance as proved by sedimentological studies (Collinson and Banks, 1975). The youngest sandstone in the formation is the Rough Rock (RR), a northerly sourced, deltaic, pebbly, coarse-grained sandstone. The top of the formation is defined by the base of the Subcrenatum (Six-Inch) Marine Band, which defines the base of the Pennine Coal Measures Group. The formation is about 245 m thick.

Further information and descriptions of the sandstones, coals and marine bands within the Millstone Grit Group are given in (Figure 4) and (Figure 5) respectively.

Westphalian

Rocks of the Pennine Coal Measures and Warwickshire groups, of Westphalian age, crop out over much of the north and east parts of the district. During Westphalian times deposition occurred in a delta plain environment that was above sea level for much of the time and land floras were abundant.

The Pennine Coal Measures Group is divided into Lower, Middle and Upper formations, with all present in the district (Figure 1), (Figure 6a) and (Figure 6b). The group rests conformably on the Millstone Grit Group, and the base of the Pennine Lower Coal Measures Formation (PLCM) is taken at the base of the Subcrenatum Marine Band. Exposure of the Coal Measures Group is generally poor but informative sections can be seen in several former quarries and brick pits, most notably around Oldham [SD 941 041]. The Coal Measures consist of cyclic sequences of interbedded mudstone, siltstone and sandstone with subordinate coal and seatearth. Mudstone is dark grey to black, weathering to orange-brown, planar laminated and micaceous, or massive. Commonly, mudstone contains nonmarine bivalves, for example the Dubhill Mussel Band (not shown on the map face), whereas others are typically black and contain a marine fauna which may be used as both a chronostratigraphical and stratigraphical indicator. Marine bands are generally only a few centimetres thick but may rarely attain thicknesses of up to one metre. They can be recognised across large areas as they are believed to represent eustatically controlled flooding events and are regarded as important marker horizons. The Subcrenatum, Listeri, Amaliae, Vanderbeckei, Aegiranum (AGMB) and Cambriense marine bands are recognised across the district. The Maltby, Haughton, Sutton, Edmondia and Shafton marine bands have also been recognised in modern boreholes drilled for coal exploration in the concealed coalfield west of Eccles [SJ 760 980]. The Pennine Middle Coal Measures Formation (PMCM) extends from the base of Vanderbeckei Marine Band to the base of the Cambriense Marine Band. This interval also includes the Aegiranum Marine Band, marking the Duckmantian–Bolsovian regional stage boundary. The Pennine Upper Coal Measures Formation (PUCM) extends from the base of the Cambriense Marine Band to the diachronous base of the Warwickshire Group. Additionally, Lingula bands have been proved which may correlate with the Langley and Burton Joyce marine bands found elsewhere in the Pennine basin. The mudstone units within the cycles are commonly gradationally overlain by siltstone, which is typically medium grey with ripple cross-lamination, and parallel lamination and commonly contains plant debris. Siltstone grades both vertically and laterally up into sandstone. The sandstone units (Figure 4) and (Plate 1) commonly form positive, mappable, topographical features, and are thus distinguished on the map.

The sandstone units can be thin and laterally impersistent, but many are extensive and basinwide. Sandstone is mainly medium grained, but varies from fine to coarse grained, and comprises subangular to subrounded quartz and feldspar grains with a variable mica content. The sandstone is grey where fresh but weathers to yellowish brown. Some sandstone bodies are greenish in colour, notably the Old Lawrence Rock (OL; Pennine Lower Coal Measures Formation), and were derived from a western sediment source (Chisholm et al., 1996). Sedimentary structures present in sandstone units include planar lamination, cross-bedding and ripple cross lamination together with lenticular bedding. Coalified plant fragments are common, as are trace fossils locally.

Seatearths are palaeosols which are characterised by the presence of rootlets. Palaeosols occur in all lithologies, and are referred to as ganister where developed in sandstone, and fireclay where they are formed in mudstone. In general, pedification has destroyed the primary sedimentary structures. Seatearths are typically succeeded by coal seams which cap upward-coarsening sedimentary cycles. Many coal seams are extensive, and can develop regionally, but they vary laterally in thickness and composition, particularly by the number of 'dirt' (mud-prone) partings present within a seam. The more important coal seams within the district are shown in (Figure 5). Modern correlation techniques have greatly improved understanding of how coals across the district relate to those developed in surrounding areas (e.g. Wigan and St Helens). Astandardised nomenclature promulgated by the former National Coal Board (Western Area) (Ridgway, 1983) has been used for rationalising coal seam names across the district.

The Warwickshire Group, which conformably overlies the Pennine Upper Coal Measures strata, is divided into the Etruria Formation and overlying Halesowen Formation. The base of the group is diachronous across the district and represents a gradual change from dominantly marine to fluvial deposition. These Asturian (Westphalian D) strata of the Manchester district are the youngest Carboniferous strata preserved within the South Lancashire Coalfield.

The Etruria Formation (Et) (comprising the former 'Ardwick Marls', and the lower part of the 'Ardwick Group' of Tonks et al., 1931) is a sequence dominated by mottled brown, red, purple, green and grey, poorly bedded mudstone (Aitkenhead et al., 2002). The presence of palaeosols is characteristic of the formation, recognised by the disruption of primary sedimentary structures by pedogenesis, and a mottled appearance, commonly after rootlets. The unit is thickest within the Bradford Inlier, which preserves about 90 m; further west up to 80 m are preserved, although in many instances much of the formation has been removed by erosion during the early Permian. Faunas recovered elsewhere from the Etruria Formation imply that a timeline representing the Bolsovian– Asturian boundary may occur at or near the top of the formation.

The Halesowen Formation (Ha) comprises the upper part of the former 'Ardwick Group' of Tonks et al. (1931), and represents a partial return to 'Coal Measures' type sedimentation. The boundary with the underlying Etruria Formation is taken at the onset of grey-bed sedimentation on the primary red beds of the Etruria Formation. This corresponds locally with the base of the Holt Town Sandstone Bed (HTS), an impersistent sandstone; where this is absent, the junction with the Etruria Formation can be difficult to identify, especially where the Halesowen Formation is reddened. In central England, the boundary can be proved by sandstone and clay mineral variations (e.g. Besley and Cleal, 1997), although this approach has not been tested in the south Lancashire Coalfield.

The Halesowen Formation is dominantly composed of mudstone, with up to twelve thin limestone beds, including the Great Mine Limestone (GML) (Roeder, 1890). The limestone beds were formerly exposed in sections along the River Medlock at Beswick [SJ 860 983] and have yielded Spirorbis, ostracods and fish debris (Jones, 1938).

Key localities

Permian and Triassic

Permian and Triassic strata at outcrop in the Manchester district include representatives of the Appleby, Cumbrian Coast and Sherwood Sandstone groups. The lower Permian Appleby Group is represented by the Collyhurst Sandstone Formation (CS) which crops out in the southern part of the district and lies unconformably on the Coal Measures Group. During early Permian times, about 300 to 275 million years ago, fault-bounded half-grabens developed and aeolian sedimentation dominated. The thickness of the formation varies up to about 260 m, with at least some of this variation being related to synsedimentary faulting (Tonks et al., 1931; Poole and Whiteman, 1955; Aitkenhead et al. 2002). The formation comes to crop in the eastern part of the district around Failsworth [SD 908 000], and in a series of fault blocks between Droylsden [SJ 890 990], Whitefield [SD 810 064] and Blackmoor [SD 680 005]. The sandstone is red and orange, fine to medium grained, and has been interpreted as being dominantly aeolian (Plant et al., 1999) or having a mixed aeolian and fluvial origin (Aitkenhead et al., 2002). There are currently no exposures of the unit in the district; it was formerly exposed in the type area in the River Irk at Collyhurst [SJ 851 998] and in the River Medlock at Clayton Bridge [SJ 894 996].

The Cumbrian Coast Group is late Permian in age and is represented by the Manchester Marls Formation (MM), which occurs in the southern part of the district. During late Permian times, about 270 to 250 million years ago, the district lay close to the eastern shore of the Bakevellia Sea. Red mudstone, partly marine in origin, with sporadic thin beds of limestone and siltstone were deposited. The formation thickens eastwards from 7 m in the Trafford Park area to over 70 m at Ashton-under-Lyne, and is conformable on the Collyhurst Sandstone,or locally oversteps the Collyhurst Sandstone to rest unconformably on the Pennine Upper Coal Measures Formation or Warwickshire Group. The lower part of the formation is fossiliferous, and has yielded a limited marine fauna (Aitkenhead et al., 2002). The upper part was formerly exposed at Collyhurst [SJ 846 996], and is usually well defined in boreholes.

The overlying Triassic Sherwood Sandstone Group represents a return to continental style sedimentation, with sediment initially supplied by broad fluvial systems that were sourced from the Varsican foldbelt to the south. The distal location of the south Manchester region resulted in a fine to medium-grained, occasionally pebbly sandstone sequence being deposited; subsequently, deposition became increasingly aeolian. The Sherwood Sandstone Group comprises red-brown, orange and buff coloured sandstone with subordinate beds of red-brown mudstone. Sandstone units within the Sherwood Sandstone may be strongly cross-bedded or massive (structureless). The group has three distinguishable formations in the Manchester district, which are identified primarily by sedimentary facies associations; age-diagnostic fossils are absent, precluding a biostratigraphical classification. The lowest of these, the Kinnerton Sandstone Formation (KnS), comprises up to 50 m of red-brown sandstone of aeolian origin and is known only from boreholes to the west of Eccles.

The formation probably ranges from late Permian to Early Triassic age and is laterally equivalent, in part, to the Manchester Marls. The Chester Pebble Beds Formation (CPB) attains a maximum thickness estimated to be in the region of 440 m. The formation is exposed at Little Bolton Quarry, Eccles [SJ 787 985], where a thinly laminated aeolian sandstone is overlain by a trough cross-bedded fluvial sandstone; mudstone beds, which are also preserved in this section, are interpreted as deposition in abandoned river channels or perennial lakes.

The Wilmslow Sandstone Formation (WlS) forms rockhead in the southern part of the area, and is estimated to reach a maximum thickness of 275 m at Urmston [SJ 770 394]. The formation is not currently exposed in the area. Elsewhere in the Cheshire Basin, the basal part of the formation comprises a well-sorted, orange and pale buff, fine- to medium-grained sandstone that shows large-scale low-angle cross-bedding, with sporadic well-cemented sheet-flood sandstones. The unit was deposited as large aeolian dunes that formed on the interfluves of a major braided-river system. The junction between the Chester Pebble Beds and Wilmslow Sandstone shown on the 1:50 000 Series map is conjectural, based on the thicknesses of the units proved in the Stockport area (Taylor et al., 1963).

Key localities

Chester Pebble Beds Formation: Little Bolton Quarry [SJ 787 985] (Plate 4); River Irwell [SJ 834 984] and [SD 770 045]; Castlefield [SJ 832 976] (front cover).

Quaternary

Throughout the Pleistocene (2.6 Ma to 11.5 ka) the district has been repeatedly covered by ice during successive glacial episodes. However, the superficial deposits which fill the Manchester embayment, an eastward extension of the Cheshire Plain, are predominantly glacigenic deposits of probable late Devensian (Dimlington Stadial) age and derived from the Irish Sea ice-sheet, although the high ground of the Rossendale Plateau to the north and the Pennines to the east contributed locally sourced ice (Figure 7). The Dimlington Stadial is considered to be a post 26 ka event (Chiverrell et al., 2004), but Bowen et al. (2002) have proposed that a highly mobile and climatically sensitive ice mass, known as the British and Irish Ice Sheet, existed in the Irish Sea basin and adjacent onshore areas throughout much of the Devensian. The postglacial, Holocene fluvial system was influenced by the presence of glacigenic deposits effectively blocking the original water courses, and new channels were cut through bedrock; low lying areas developed extensive peat mosses.

Much of the early work on the Quaternary deposits in the district during the late 19th and early 20th centuries supported the classic 'tripartite sequence' (Upper Boulder Clay– Middle Sands–Lower Boulder Clay) first proposed by Hull (1864) in the Manchester area; it was suggested that there was more than one glacial advance across the area. The tripartite sequence model culminated in the work of Poole and Whiteman (1961, 1966) who not only envisaged multiple glaciations but also extensive lacustrine development with an extended Lake Lapworth. As understanding of lowland glacier dynamics improved and more reliable dates were obtained from the organic deposits at Chelford [SJ 810 730], to the south of the district in Cheshire, doubt was cast on this model and by the 1980s a single glacial episode theory for the late Devensian was accepted (e.g. Jackson et al., 1983; Earp and Taylor, 1986). Correlation of well-defined moraines within the Cheshire Plain to global climatic events (Bowen et al., 2002) has allowed more comprehensive overviews of the glacial history of the district (e.g. Delaney, 2003; Thomas, 2005; Crofts, 2005a, and references therein).

Pre-late Devensian landscape

There are no deposits proved to be of pre-late Devensian age within the Manchester district, but a series of buried palaeochannels have been identified from extensive borehole records (Figure 8). These formerly drained from the Rossendale plateau and Pennines to the north and east respectively, but have been concealed by later glacigenic deposition. The most extensive are the proto-Medlock and proto-Roch which underlie Oldham and Rochdale/Middleton, respectively. In the south-west of the district, an extensive westward draining system has also been identified between Urmston and Eccles and underlying Chat Moss, which may be part of a proto-Irwell–Mersey drainage system.

Southward draining palaeovalleys of the Roch–Irk system underlying Middleton, and a middle Irwell channel between Radcliffe and Clifton Junction, may indicate the dominant drainage direction immediately prior to the advance of the late Devensian ice into the Manchester embayment. As the Irish Sea ice front advanced north-eastwards, the original drainage system was buried and topographical changes, as the ice decayed, resulted in the subsequent postglacial drainage pattern reflecting in part a more ice-marginal system.

Early late Devensian

To the north of the district, there is clear evidence of ice advancing south-eastwards across the North Lancashire plain towards Rossendale (Longworth, 1985) and southwards, depositing a distinctive limestone-rich till termed the Ribblesdale Till (Jowett, 1914; Wright et al., 1927). However, this distinctive deposit has not been proved south of Rawtenstall [SD 810 230] to the north of the district. The thin tills which mantle the hill slopes north of Bolton and east of Oldham may reflect the movement of locally sourced ice southwards and westwards, from the immediately adjacent high ground of Turton Moor/Scout Moor and the Pennines respectively (Crofts et al., 2010). There is no clear evidence for the limit of any such local ice streams due to the later influence of the Irish Sea ice-sheet, which at this time was probably advancing southwards and eastwards across the Irish Sea Basin and Cheshire lowlands, entering the district from the west along the Mersey valley.

Late Devensian

During the glacial maximum (about 26 ka BP) and retreat the Irish Sea ice deposited a significant thickness of diamict and sand complexes. A large moraine complex developed between Pilsworth and Rochdale indicating the probable limit of this ice advance against the Rossendale Plateau. Northwards, the upper reaches of the Irwell, Eagley and Roch catchments appear, by this stage, to have been ice free, perhaps indicating an early disintegration of any small ice cap on Tuton Moor/Scout Moor. These rivers, together with eastward- and westward-draining ice-marginal channels, such as the Croal Channel west of Bolton [SD 700 087] supplied water to a large ice-marginal lake system between Bolton and Bury. Jowett (1914) first proposed that a lake existed in this area as the final phase of deglaciation of the Rossendale plateau whilst Tonks et al. (1931) envisaged 'Lake Bolton' as part of a much larger glaciolacustrine system extending southwards and linked to Lake Lapworth. The current survey, in association with digital terrain modelling, suggests Lake Bolton was a relatively small ice marginal lake (Crofts, 2005b). Oscillations in the ice front allowed ice marginal drainage from the upper Roch and Irwell basins and formed the rock gorges at Marland [SD 875 125], Fairfield [SD 835 115] and Nob End [SD 755 065] with water flowing in to Lake Bolton. Any oscillation of the ice front southwards would have allowed the Croal and upper Irwell catchments to merge and as a consequence to develop an extended lake, Lake Bolton-Bury (Crofts, 2005b).

With progressive deglaciation, extensive spreads of glaciofluvial outwash deposits developed, cutting through moraines and in many instances reworking glacial deposits into thick cross-bedded sand and gravel complexes, such as that draining through the Castleton/Slattocks gap [SD 885 110]. In Central Manchester, extensive sand deposits with a gentle gradient of about 1 in 300 towards the south-west, and overlain in part by poorly consolidated clay, may indicate a series of ice-marginal channels or an unconfined outwash plain developed against the retreating ice front. Elsewhere in the district, outwash deposits were entrained in valley sandar, such as the deposits in the Irwell [SJ740 950] and Irk [SD 875 056], the surfaces commonly at successively lower elevations as the base level dropped. Some renewed sandar activity may have occurred during the Loch Lomond Stadial (11 000 BP), as it is probable that extensive snow melt occurred during summer months from the Rossendale Plateau and Pennines, releasing large volumes of water down the valley systems.

The main deposit of the late Devensian glaciation is till, the material eroded, transported and deposited directly from the ice-sheet. This comprises a poorly sorted deposit varying from gravelly, sandy, silty clay to sandy, clayey gravel with individual clasts ranging up to boulder size. Two distinct types have been recognised in the district. South of Bury and Bolton, till associated with the Irish Sea ice typically comprises an overconsolidated, poorly sorted, purplish brown silty clay with rocks from the Lake District, Carboniferous limestone, Carboniferous sandstone and Coal Measures, and has been designated as the 'Stockport Formation' (Worsley 1967). This till thins and the proportion of Coal Measures material increases progressively northwards reflecting the character of the underlying bedrock. North of Bolton, thin till on the hillslopes dominantly comprises Coal Measures material in a stiff grey clay matrix. This deposit was either derived from the higher ground to the north and deposited by locally sourced ice moving southwards, or by the Irish Sea ice at its acme when its basal sediment load was dominated by material from the local bedrock.

Large-scale constructional landforms developed at the margin of the Irish Sea ice-sheet at the southern edge of the Rossendale plateau. These typically form a complex of ridges and kettle-kame topography, and were mentioned briefly by Tonks et al. (1931) and previously mapped by the BGS largely as sand. These landforms are attributed to an oscillating ice margin and are now mapped as morainic deposits . Three distinct morainic ridges are present in the district: the Pilsworth Moraine (Plate 5) between Whitefield [SD 805 650] and Heywood [SD 865 110]; the Heaton Park–Middleton Moraine (Plate 5) between Rainsough [SD 810 020] and Chadderton Heights [SD 895 075], and the Tandle Hill Moraine, between Tandle Hill [SD 900 085] and Shaw [SD 940 095].

The Pilsworth Moraine may represent either the northernmost limit of the Irish Sea ice in the district or a major oscillation in the recession southwards of the waning Irish Sea ice-sheet from the Rossendale Plateau. The ridge is up to 20 m high, approximately 7 km long and 1.5 km wide, with the rise most prominently displayed at Pilsworth Road [SD 825 092]. The lithology of the deposit is very variable, but comprises an upper sequence of contorted and overfolded sands and gravels, overconsolidated reddish brown stony clay and grey stoneless clay. A similar contorted till, formerly visible at Birch during construction of the M62, is also attributed to an oscillating ice front (Johnson, 1971). Beneath the contorted strata are undistorted ripple-laminated and parallel-laminated sands with coal and trough cross-bedded sands and gravels with Carboniferous and Lake District pebbles and coal (Plate 5). The sands and gravels may be subaerial proximal or deltaic facies, deposited on the margins of Lake Bury–Bolton prior to being overridden by a minor ice front re-advance.

The Heaton Park–Middleton Moraine marks a major halt in the southwards recession of the waning Irish Sea ice-sheet. The ridge is up to 40 m high, 10 km long and 1.5 km wide, and has a steep south-facing ice-contact slope most prominently displayed at Hilton Park [SD 815 025], Rhodes [SD 850 055] and Chadderton Heights [SD 900 070]. The lithology is variable. In the western part, there is mainly cross-bedded sand with some lenses of stony clay. Eastwards, reddish brown clay mantles the surface, although boreholes prove a complex mixture of sand, stony clay and laminated clay.

The Tandle Hill–Shaw Moraine is up to 50 m high, 3.5 km long and 1 km wide, with a steep south-facing ice-contact slope prominently displayed in Tandle Hill Park [SD 905 085] and at High Crompton [SD 930 097]. Large kettle holes occur within the ridge. The ridge comprises mainly cross-bedded sand, with lenses of gravel and stony clay, the sand having been worked locally in the past (e.g. [SD 913 093]). Locally, reddish brown clay, possibly a flow till, covers the sand. At Starkey Farm [SD 922 095] clay is the principle lithology and was formerly worked for brick clay, although the pits are now restored.

The Tandle Hill–Shaw Moraine, together with the Heaton Park–Middleton Moraine, may form part of the same complex, although no dating evidence is currently available. Crofts and Humpage (2005) tentatively correlated this morainic complex with the Ellesmere–Whitchurch–Barr Hill Moraine in the Cheshire–Shropshire lowlands (Worsley, 2005), which Bowen et al. (2002) have linked to the Heinrich II event at about 22 ka BP.

Glaciolacustrine deposits comprising laminated clay, silt and very fine sand, have been recorded as flat spreads and in boreholes at various locations across the district, including south-west of Bury [SD 790 090], at Farnworth [SD 740 060], and between Heaton Park and Middleton [SD 825 059]. Extensive glaciolacustrine deltaic deposits underlie Bolton town centre and about 20 m of sand and gravel have been recorded (Tonks et al., 1931) overlying sand and laminated clay and silt. Tonks et al. (1931) considered this to be a prograding delta sequence, with water entering Lake Bolton via the Croal Channel, now occupied by Middle Brook. Elevation data indicate a maximum water surface level of about 90 m above OD with water held up on its southern margin by the Irish Sea ice and the related Pilsworth Moraine complex. More clay-rich glaciolacustrine deltaic sediments have been proved at Stock Nook [SD 850 087] where an ephemeral lake developed between a sandy ridge north of Birch motorway services [SD 848 079] and a bedrock high at Hares Hill [SD 844 093], to the north. Further deposits occurring on the eastern margins of Chat Moss at Irlam [SJ 722 953], indicate water flowing into a standing body of water, possibly ice-dammed, prior to being overlain by glaciofluvial sheet deposits.

Undifferentiated glaciofluvial deposits of late Devensian age occur as isolated deposits and as more extensive spreads across much of the western and northern part of the district. The most extensive deposits are between Heywood and Milnrow [SD 880 120], Darn Hills [SD 830 110] and Fishpool [SD 806 098] where undulating topography, dominated by sand, forms lateral extensions to the Pilsworth Moraine. In the Irwell valley, west of Salford and in central Manchester, the sands exhibit less relief, and may correlate with extensive glaciofluvial sheet deposits recorded north and west of Manchester.

As the Irish Sea ice-sheet decayed during deglaciation, constructional features such as isolated upstanding sand-dominated mounds and ridges were deposited; these are represented by ice contact deposits. Some appear to be streamlined and may have a subglacial origin, such as some of the mounds north of the Heaton Park Moraine at [SD 839 064]. In the Croal Channel [SD 690 089] and at Farnworth [SD 730 055], mounds of sand may be ice-marginal kame deposits.

As the Irish Sea ice-sheet withdrew from the Manchester area, vast quantities of meltwater deposited extensive tracts of sand and gravel as glaciofluvial sheet deposits . A large-scale sandur plain extending from Chadderton south-westwards towards the River Mersey developed whilst farther north the valleys of the rivers Irwell and Roch and their tributaries were filled with these deposits. Incision of the Irwell gorge at Farnworth may have resulted in the development of successive glaciofluvial sheet deposit terraces in the valleys of Eagley Brook [SD 723 103] and Bradshaw Brook north of Bolton [SD 733 115] as base levels fell, whilst subsequent postglacial fluvial erosion has left the deposits in the lower Irwell valley south of Eccles as a high terrace about 6 m above river level. As the postglacial drainage system became established, more confined valley sandar developed in the Irwell, Irk and Roch, which may in part be associated with a rejuvenated outwash system during the return to cold climatic conditions of the Loch Lomond Stadial. Further spreads of sheet deposits occur in river valleys draining the western Pennines, including the Tame through Dukinfield [SJ 935 970] and the River Beal at Newhey [SD 935 114]. Deposits of sand and silt spread from what are now minor streams on hillsides north of Bolton [SD 695 124], indicating much greater water flow in the past. Though designated as glaciofluvial subaqueous fan deposits, these deposits are thought to have a significant subaerial component, possibly associated with ephemeral bodies of water that were ice dammed.

Postglacial

Since the end of the last glaciation, slopes have been modified, the modern Holocene river system has become established and, in the south-west of the district, extensive peat 'mosses' developed on the glacigenic deposits. The mosses, in particular Chat Moss [SJ 710 960], formed from the amalgamation of several shallow peat basins and in recent years, as the peat surface has deflated as a result of agricultural practices and continuing peat extraction, ridges of till have become exposed. As much of the Manchester district lies within a major conurbation, extensive land surface modification has occurred.

Immediately following the ice retreat, widespread seasonal freezing and thawing under periglacial conditions modified many of the landforms and remobilised sediment by solifluction, the downslope movement of material by frost creep or saturated flow, to form deposits of head . These comprise highly variable gravelly, sandy, silty clay with clasts in a silty clay matrix. Head deposits are ubiquitous, but have only been recorded where they form a significant thickness and have distinct topographical expression; hence much of the soliflucted till has not been distinguished on the map. Head is most clearly developed in the Croal Channel [SD 674 090] and in the valley of the Whittle Brook [SD 824 083] incised through the Pilsworth Moraine. Head development has also occurred on bedrock in the foothills of the Pennines in the east of the district.

During the Holocene, post 11 500 yr BP, the modern drainage system became fully developed, with each river initially establishing a broad braid plain in the valley floor. Repeated river downcutting, in response to isostatic re-adjustment and postglacial regrading, has left former braid plain deposits preserved as elevated river terrace deposits, comprising stratified sand and gravel. Two terrace surfaces are visible in the upper and middle Irwell valley, but terraces are less well developed elsewhere. Gently sloping spreads of alluvial fan deposits, also comprising stratified sand and gravel, accumulated where steeper graded tributaries emerge into the main valleys, the best developed occurring at Moss Brook [SJ 721 986]. All these deposits are dissected by recent river deposits of alluvium, which underlie the modern floodplains and represents the area of current fluvial deposition. Alluvium typically comprises silt and organic-rich clay with beds and lenses of sand, gravel and peat. Streams were deeply incised during Holocene rejuvenation in some localities such as the upper Medlock valley (e.g. around Park Bridge [SD 947 002]) (Plate 6).

Small areas of lacustrine deposits comprising organic rich, partly laminated, silt and clay have accumulated in lakes and hollows on poorly drained ground, such as on till at [SD 952 027] and [SD 958 013]. Lacustrine deposits were further identified in boreholes in low-lying ground north of Middleton [SD 847 067] and may underlie some of the peat deposits across the district. As vegetation was re-established under more temperate climatic conditions, deposits of peat accumulated in areas of restricted drainage. Extensive mosses, locally over 3 m thick, all of which are underlain by till, developed at Clifton Moss [SD 750 041], Ashton Moss [SJ 920 990] and most significantly at Chat Moss [SJ 710 970].

Chat Moss is a large, raised mire complex covering approximately 2500 ha. Rather than being a single domed mire, it originated from at least five centres of peat formation separated by ridges in the underlying till surface, and thus may best described as a ridge-raised mire (Wilkinson and Davis, 2005). Peat accumulation was initiated in the deepest hollows probably during the Late Glacial–Interglacial transition, and by 10 000 BP there was extensive peat accumulation associated with poor fen plant communities. Ombrotrophic mire communities dominated by cotton grass (Eriophorum) were widespread by 8000 BP, but Sphagnum dominated by about 3700– 3400 BP, before giving way to heathers, grasses and sedges around 2500–2200 BP. Pollen analysis and literary accounts suggest that before systematic drainage, Chat Moss was periodically prone to 'bog bursts', exposing waterlogged black peat at the surface. These bursts may reflect intense storm events, or prolonged periods of poor climatic conditions, such as those prevailing during the Little Ice Age (approximately AD 1450–1890) when raised groundwater conditions may have influenced the mire (Davis and Wilkinson, 2005). The accumulation of peat in upland areas also occurs in the district, for example at Crompton Moss [SD 964 103].

Landslides are present across the district, particularly where glacigenic sediments on oversteepened valley sides have been undercut by meandering rivers and streams, such as at Higher Broughton [SD 822 016] (Harrison and Petch, 1985) and at [SD 782 050] in the Irwell valley. Larger, individual landslides affect bedrock on the rising ground in the east of the district, such as those around the Ogden reservoirs [SD 967 122; SD 953 118].

Key localities

Artificially modified ground

During the Holocene, the landscape has been extensively modified by human activity, the more so as the district has been heavily industrialised since the early nineteenth century. Excavated areas of worked ground occur across the district, mainly large sandstone quarries (e.g. [SJ 787 985]), former brickpits [SD 941 041] and sand pits; sand is currently worked at Pilsworth [SD 826 090] and Town Lane [SJ 687 989].

Made ground, commonly of colliery or quarry spoil, or domestic refuse of variable composition and thickness, covers extensive areas in the Irwell valley [SD 800 020], [SJ 755 965], Salford Docks [SJ 805 970], central Manchester [SJ 870 990], Greenheys [SD 705 043], and at Middleton Junction [SD 890 045], where it has been used for land-raising fill for development. Trafford Park [SJ 7890 970] has been constructed on a large area of raised fill, typically 2–3 m thick, but locally in excess of 8 m; many other smaller areas of made ground occur across the district. Where former quarries and pits have been backfilled with overburden and waste material, these are shown as areas of infilled ground. Some of the largest of these areas are the former surface mine (opencast) coal sites at Hulton [SD 695 050, SD 687 065], and former sand pits at [SJ 825 095], [SJ 895 097] and [SD 835 106]. Large brickworks formerly extracted glacigenic deposits at several locations close to Manchester city centre, including Newton Heath [SD 875 003], Openshaw [SJ 890 978], Strangeways [SJ 838 996] and Moss Side [SJ 845 950].

Other human activity has involved the drainage and reclamation of the peat mosses which started in the mid 18th century. Also by this time, colliery waste was being dumped on Chat Moss, followed by the dumping of 'night soil' from the growing towns and cities. The construction of the Liverpool and Manchester Railway across Chat Moss in 1829 involved the digging of four parallel drains for 6.5 km, and when completed, allowed the transport of waste to Chat Moss to increase. The domestic cutting of peat has a long history, and by the early 20th century, industrial extraction was well established, a process that continues today. The combined effects of drainage and peat working have resulted in a significant lowering of the peat surface; undrained woodland areas of Chat Moss may stand over two metres above the surrounding area (e.g. [SJ 717 965]), and at Larkhill [SJ 705 953] the ridges of till which defined the original peat basins are exposed.

Disturbed ground is associated with ill-defined surface workings such as shallow sandstone quarries and areas of bell pits. Landscaped ground comprises areas where the original surface has been extensively remodelled, but where it is not feasible to delineate areas of cut or made ground (for example, levelled industrial sites). Most urban areas are associated with landscaped ground. The 1:50 000 scale geological map does not show areas of landscaped and disturbed ground, though they are delineated on the constituent 1:10 000 scale geological maps.

Chapter 3 Applied geology

Within the Manchester district, applied geological factors are an important consideration within the urban, industrial and rural planning processes. A history of coal mining, quarrying, brickmaking and associated heavy industry has left a legacy of variable and difficult ground conditions. The interplay between natural geological and artificial, man-made factors should be considered at an early stage in the planning process so that appropriate remediation or mitigation measures can be taken prior to a site's development (Hough et al., 2003). Geological and geotechnical information may also be used to bring marginal land into productive use and to identify opportunities for development, particularly in respect of leisure, recreation and protection of sites of nature conservation interest. The key issues for the Manchester district are discussed below.

Energy

Coal has been worked on a large scale in the district from the Pennine Lower and Middle Coal Measures formations. Workings were also active in the Upper Coal Measures (notably within the Bradford Coalfield) and on a smaller scale in the Rossendale Formation (Sand Rock Coal) in the east of the district. Deep coal mining ceased in 1991 with the closure of Agecroft Colliery at Pendlebury; Cutacre Reclamation at Greenheys [SD 705 041] is currently the only active surface mine (opencast) site operating in the district. The main factors hindering further extraction are the thickness of overburden including natural Quaternary deposits and man-made deposits, sterilisation by urban development, conflicts for land use and possible further detrimental effects on the landscape.

The prospect of economic abandoned mine and coalbed methane resources is not particularly good, probably due to a combination of former coal mines being either flooded, or providing poor yields (Glover et al., 1993; Kirby et al., 2000). However, investigations are taking place in the area immediately to the south-west of this district, around Warrington for coalbed methane.

The south Lancashire region was targeted for oil and gas exploration during the 1970s and 1980s, with the most likely prospects being intra-Carboniferous plays. Despite favourable source rock being located beneath the district (Kirby et al., 2000), the Heywood No. 1 Borehole (completed by BP in 1984) yielded only minor hydrocarbon shows. Shale gas is currently being explored and evaluated from Namurian and Visean mudstones to the north-west of the district. Workings for peat by mechanical milling are currently active at Chat Moss [SJ 690 950], [SJ 712 966], [SJ 715 980], [SJ 690 973]. Peat has been commercially worked in the district since the 1700s, initially for fuel, shortly after the first attempts to drain Chat Moss.

Mineral resources

The principal mineral resources of historical importance in the district are given in (Figure 9), with further detail by Minchin et al. (2006).

Sand and gravel, used in concrete and as a constructional fill, is worked from superficial deposits extensively in the area south-east of Bury [SD 800 120], and is extracted from weathered Chester Pebble Beds Formation (Sherwood Sandstone Group) at Morleys Hall near Town Lane [SJ 687 989]. Abandoned workings are extensive between Royton [SD 915 080] and Rochdale [SD 880 135], where sand and gravel was worked for aggregate and to provide fill during motorway construction. Most of the Carboniferous sandstones are too weak or porous to be suitable as a roadstone or concrete, but may be appropriate for fill or for the production of sand or crushed rock aggregate. Sandstone from the Old Lawrence Rock is currently extracted at Harwood [SD 746 124]; notable sites of former workings include Little Bolton [SJ 787 985] where the Chester Pebble Beds were quarried, and Collyhurst [SD 853 001], where the Worsley Delf Rock was worked as a building stone.

Mudstone has been worked for brickmaking and dam construction, mainly from within the Pennine Lower Coal Measures Formation. Harwood [SD 746 124] is the only pit currently active, with clay from the Pennine Lower Coal Measures used for making facing, engineering and paving bricks (Minchin et al., 2006). Former workings for brick clay within the Coal Measures Group are present, for example at Lowside Brickworks [SD 941 041]. In addition, clay-rich units within till have been worked to produce bricks in the Newton Heath [SD 875 005], Openshaw [SJ 890 978], Strangeways [SJ 838 996] and Moss Side [SJ 845 950] areas.

Limestone was formerly extracted from the Great Mine Limestone of the Halesowen Formation via a series of shafts in the Beswick area [SJ 863 976]; extraction continued until at least the late 1880s. The limestone produced slow-setting cements that were used in the lining of colliery shafts (Tonks et al., 1931). Limestone was also extracted from the Manchester Marls Formation at Blackmoor [SD 680 003], and in about 1800, to the south-west of Worsley [SJ 741 997] (Hull and Slater, 1862).

Quarries and pits that remain open represent an important resource as they provide a suitable depository for waste, may be re-opened for further mineral extraction, or as in the case of Lowside Quarry [SD 941 041], may provide educational, recreational or wildlife value. However, they can also be a constraint to development as steep rock faces may be unstable. Quarries and pits within the district have been worked mostly for sandstone, mudstone and aggregate.

Engineering ground conditions and environmental geology

The three important ground conditions relevant to construction and development in the district are the suitability of the ground to support structural foundations; the ease of excavation, and the use as engineering fill. A comprehensive study of ground conditions and geohazards in central Manchester and Salford, and the value of a 3D geological model in their assessment, is given by Bridge et al. (2010). Geological issues relevant at the planning stages of site development are summarised for the main engineering geological units in the district in (Figure 10).

Important potential geohazards within the district include subsidence and acid mine-drainage problems due to previous shallow and deep mining for coal; leachate migration; slope stability and mass-movement; flooding of alluvial ground, and gas emissions related to both landfills and the underlying geology (including natural radon).

Subsidence and acid mine-drainage problems are associated with abandoned mine workings present in the north and east of the district on the southern edge of the South Lancashire Coalfield. The smaller Bradford Coalfield forms a structurally isolated inlier, surrounded by Permo-Triassic rocks, and bound to the east by the Bradford Fault. This inlier was worked from Bradford Colliery [SJ 871 985] until its closure in 1968. Ground instability caused by the collapse of shallow coal seams worked by pillar and stall methods and their associated roadways may cause subsidence problems. There are numerous disused shafts and adits present in the district associated with former deep and shallow workings for coal and limestone.

Within the Manchester district some structures and infrastructure have been affected by subsidence. Areas around Swinton [SD 775 015] and near the City of Manchester Stadium (located on the former Bradford Colliery site) have been heavily affected by subsidence in the past (Douglas, 1985). Arup Geotechnics (1991) provided a review of mining subsidence in the UK. As well as subsidence, coal mining has caused some watercourses in this district to become contaminated and polluted by acidic mine waters. When exposed to oxygen these waters form an ochre-red deposit in the water, most notably developed along the Bridgewater Canal at Worsley Delf [SD 748 005]. The Coal Authority provides information about any local coal mining subsidence, shaft and adit locations and acid mine-drainage and should be consulted prior to development in a coalfield area (see Information Sources).

Leachate migration may be a problem where groundwater percolates through waste and becomes enriched in potentially harmful soluble components. The resultant leachate may migrate laterally in permeable superficial deposits or bedrock adjacent to the site, according to the depth of the unsaturated zone. This is potentially a most serious hazard at landfill sites situated in deposits in hydraulic continuity with aquifers in the Pennine Coal Measures and Millstone Grit groups, and may be exacerbated within areas that are highly faulted. Similar problems may be encountered with river terrace deposits and alluvium.

Slope stability and mass movement is an issue particularly where building development has extended up steep valley sides or close to steep slopes, and landslides have been identified in such localities within this district. One of the biggest is the Cliff landslide [SD 822 016], which occurs on the banks of the River Irwell at Higher Broughton, and has caused damage to surrounding houses (Harrison and Petch, 1985). This landslide is a complex mass-movement feature formed in unconsolidated glacial deposits. Landslides in similar geological settings are also present further upstream on the River Irwell at Hurst [SD 780 044], and along the banks of the River Roch near Whitefield [SD 800 067]. Evidence of damage to houses and infrastructure has also been identified in parts of Salford and Bury and are thought to be caused by the piping or collapse of glaciofluvial sands (Harrison and Petch, 1985).

Slopes exceeding 3° within clay-rich superficial deposits, and clay bedrock should also be considered as potentially unstable due to relict shear surfaces produced by periglacial processes (Culshaw and Crummy, 1991). Head and till deposits can also contain thinly interbedded sequences of sands and clays, which may give rise to springs and high confined pore pressures, resulting in a loss of strength, and thus making these deposits prone to slope failure.

Flooding during periods of exceptional rainfall may affect low-lying alluvium adjacent to active stream and river courses. Flood-risk limits can be provided by the Environment Agency. The major river floodplains of the Manchester district include tracts of river terrace deposits and glaciofluvial sheet deposits, which are higher than the surrounding alluvium. The distribution of these deposits and the alluvium should therefore form the basis for any plan to manage flood risk and any protection measures that may be required in these areas. In addition many areas of alluvium have been raised to higher levels by the import of man-made materials; during the 1800s, quarry spoil and cinders were dumped into many of the watercourses, which resulted in a drastic reduction in the capacity, and caused the flooding of the River Medlock at Pin Mill Brow [SJ 856 978] in 1872 (Plate 7).

Gas emissions of methane, carbon dioxide, and carbon monoxide may occur naturally from concealed Coal Measures strata, or from the decomposition of artificial material in landfill sites. These gases can migrate considerable distances through permeable or fractured strata and may accumulate in enclosed spaces such as in basements, buildings, excavations, caves, mines and tunnels. High concentrations may become hazardous, especially during periods of low atmospheric pressure, with methane posing a fire or an explosion hazard, and carbon dioxide and carbon monoxide causing asphyxiation and vegetation dieback. Ventilation is required in areas where accumulation of these gases may occur at high concentrations.

Radon is a naturally occurring radioactive gas produced by the radioactive decay of radium, which in turn, is derived from the radioactive decay of uranium. Uranium is found in small quantities in all soils and rocks, although the amount varies from place to place. Radon is released from rocks and soils, and is quickly diluted in the atmosphere, and normally does not present a hazard. However, if it accumulates in enclosed spaces such as in basements, buildings, caves, mines and tunnels it may reach high concentrations, and may pose a health hazard from the inhalation of radioactive particles.

The variation in the radon levels between different parts of the country is mainly controlled by the underlying geology with regard to the abundance of radon-producing minerals, and the ability of the gas to reach the surface through discontinuities in the rock mass and through gas pathways in any overlying superficial or artificial deposit. Within the Manchester district radon potential is generally low, with the highest radon concentration values identified on areas of exposed Lower Coal Measures Formation rocks around Oldham [SD 925 045], Shaw [SD 935 909] and Milnrow [SD 925 125]. In these areas, the Health Protection Agency can advise on the need for properties likely to require basic preventative measures.

Seismology

The Manchester district, in common with other parts of northern and central Britain, has been affected historically by minor earthquakes. During October– November 2002, in excess of 106 recorded earthquakes, with magnitudes up to 3.9 ML and intensities up to 5 on the European Macroseismic Scale (EMS), occurred with epicentres predominantly in east Manchester (Walker and Browitt, 2003). The earthquakes, which caused minor damage including shattered windows, falling tiles and small cracks in buildings, were widely felt throughout the Greater Manchester area. It is thought that the events were associated with movements on north-west–south-east trending faults within the bedrock, although as the uncertainty of epicentre location is of the order of 2 km, it has not been possible to relate the earthquakes to individual mapped faults at surface. It is likely that all events originate from a small source volume due to similarities in source mechanism and waveform signals between the various events (Baptie and Ottemoeller, 2003). Although the cause of the apparent earthquake swarm is not known, changes in local hydrogeological conditions at depth, possibly related to the cessation of deep mining, may have acted as a trigger (Gavagan, 2005). A further six minor earthquakes located in the same area as the 2002 swarm were recorded in August 2007.

Minor earthquakes might arise through reactivation of faults by undermining, when general subsidence effects may be concentrated along them. Underground mining has ceased in the district, and although minor residual subsidence may still occur, it is increasingly unlikely that this will result in significant fault reactivation.

Water resources

Reservoirs in upland areas and incised valleys form a source of industrial and domestic water supply for towns in the north of the area such as Bolton, Bury, Heywood and in the east of the district notably Oldham and Ashton-under-Lyne (Tonks et al., 1931). Manchester draws the majority of its needs from the Lake District, transported by aqueducts (Stone et al., 2010). In the past, industrial need has been supplemented by boreholes in the Permo-Triassic sandstones particularly in Manchester and Salford.

Sands and gravels within river terrace and glaciofluvial deposits and thicker Carboniferous sandstone units may form minor aquifers within the district.

Conservation sites

The geological heritage of the district forms a resource for tourism, education and scientific research, and is also a consideration for planning and development. Some sites are in natural sections while others are located in active as well as disused quarries and pits. Sites of Special Scientific Interest in the district for geological importance, as designated by Natural England, include:

Additional sites of geological impor tance in the district are designated as Regionally Important Geological and Geomorphological Sites (RIGS) (also known as 'Local Geological Sites'), identified by locally developed criteria (see http://wiki. geoconservationuk.org.uk). Sites designated by the Joint Nature Conservation Committee (JNCC) that are conserved for their geological value are detailed in the appropriate Geological Conservation Review Series publication (e.g., Cleal and Thomas, 1996).

Information sources

Further information held by the British Geological Survey relevant to the Manchester district is listed below. Much of the BGS data holdings are now available through the OpenGeoscience website www.bgs. ac.uk/opengeoscience/. Enquiries concerning geological data for the district should be addressed to the Manager, National Geological Records Centre, BGS, Keyworth. Geological advice for the area should be sought from the Chief Geologist (England), BGS, Keyworth. Searches of indexes to these and many other data collections can be made on the Geoscience Index System in BGS libraries or by accessing the Geoscience Data Index (GDI) via the BGS website www.bgs. ac.uk. BGS maps, books and reports relevant to the district may be consulted at BGS and some other libraries. They may be purchased from the BGS sales desk, or via the BGS shop, accessible through the BGS website.

Maps

BGS books and reports

Aitkenhead, N, Barclay, W J, Brandon, A, Chadwick, R A, Chisholm, J I, Cooper, A H, and Johnson, E W. 2002. British regional geology: the Pennines and adjacent areas (Fourth Edition). (Keyworth, Nottingham : British Geological Survey.)

Tonks, L H, Jones, R C B, Lloyd, W, and Sherlock, R L. 1931. The Geology of Manchester and the South-east Lancashire coalfield. Memoir of the Geological Survey of Great Britain, Sheet 85 (England and Wales).

Plant, J A, Jones, D G, and Haslam, H W (editors). 1999. The Cheshire Basin: Basin evolution, fluid movement and mineral resources in a Permo-Triassic rift setting. (Keyworth, Nottingham: British Geological Survey.)

Kirby, G A, Baily, H E, Chadwick, R A, Evans, D J, Holliday, D W, Holloway, S, Hulbert, A G, Pharoah, T C, Smith, N J, Aitkenhead N, and Birch, B. 2000. The structure and evolution of the Craven Basin and adjacent areas. Subsurface Memoir of the British Geological Survey.

Bridge, D McC, Butcher, A, Hough, E, Kessler, H, Leliott, M, Price, S J, Reeves, H J, Tye, A M, Wildman, G, And Brown, S. 2010. Ground conditions in central Manchester and Salford: the use of the 3D geoscientific model as a basis for decision support in the built environment. British Geological Survey Research Report, RR/10/06.

Biostratigraphy

There is a collection of internal BGS biostratigraphical reports, details of which are available on request from the Chief Curator, BGS Keyworth.

Documentary collections

Basic geological survey information, which includes 1:10 000 or 1:10 560 scale field slips and accompanying field notebooks, are archived at the BGS.

Boreholes and shafts

Geological data for many boreholes and shafts in the district are catalogued in the BGS archives at Keyworth. For further information contact: The Manager, National Geosciences Record Centre, BGS, Keyworth.

Mine plans

BGS maintains a collection of plans of underground mines for coal and other minerals.

Geophysics

Gravity and aeromagnetic data are held digitally in the national Gravity Databank and the National Aeromagnetic Databank at BGS, Keyworth. A limited amount of seismic reflection data is also available for the district.

Hydrogeological data

Hydrogeological data on water boreholes, wells and springs and aquifer properties are held in the BGS database at Wallingford.

BGS Lexicon

Definitions of named rock units shown on BGS maps, including those shown on the 1:50 000 Series Manchester Sheet 85, are held in the BGS Lexicon of named rock units, which can be accessed on the BGS website.

Material collections

Enquiries concerning BGS material collections should be directed to the Chief Curator, BGS Keyworth.

Palaeontological collection

Macrofossils and micropalaeontological samples collected from the district are held at BGS Keyworth.

Petrological collections

Petrological samples collected from the district are held at BGS Keyworth.

Geochemical samples

A database of stream sediment and water samples collected from the district are held at BGS Keyworth.

Borehole core collection

Samples and entire core from a small number of boreholes in the Manchester district are held by the National Geosciences Record Centre, BGS, Keyworth.

BGS photographs

Copies of these photographs used in this report are deposited for reference in the BGS Library, Keyworth; prints and transparencies can be supplied at a fixed tariff. Part of the photographic archive can be accessed via the BGS website.

Other relevant collections

Mine abandonment plans

Coalabandonmentplansareheldbythe Coal Authority, Mining Reports, 200 Lichfield Lane, Mansfield, Nottinghamshire, NG18 4RG. These plans are held by the Coal Authority in the public domain, and may include some plans not held by the BGS.

Fireclay abandonment plans

Fireclay abandonment plans are held by the Health and Safety Executive, Rose Court, 2 Southwark Bridge, London, SE1 9HS.

Groundwater licensed abstractions, catchment management plans and landfill sites

Information on licensed water abstraction sites, for groundwater, springs and reservoirs, Catchment Management Plans with surface water quality maps, details of aquifer protection policy and extent of washlands and licensed landfill sites are held by the Environment Agency.

Geological conservation sites

Information on the Sites of Special Scientific Interest present within the Manchester district is held by Natural England, 3rd Floor, Bridgewater House, Whitworth Street, Manchester, M1 6LT.

References

Most of the references listed below are held in the Library of the British geological Survey at Keyworth, Nottingham. Copies of the references can be purchased subject to the current copyright legislation.

Aitkenhead, N, Bridge, D Mcc, Riley, N J, and Kimbell, S F. 1992. Geology of the country around Garstang. Memoir of the British Geological Survey, Sheet 67 (England and Wales).

Aitkenhead, N, Barclay, W J, Brandon, A, Chadwick, R A, Chisholm, J I, Cooper, A H, and Johnson, E W. 2002. British regional geology: the Pennines and adjacent areas (Fourth Edition). (Keyworth, Nottingham: British Geological Survey.)

Arup Geotechnics. 1991. Review of mining instability in Great Britain. Report to the Department of the Environment, Arup Geotechnics, Ove Arup and Partners. (London: HMSO.)

Baptie, B, and Ottemoeller, L. 2003. The Manchester earthquake swarm of October 2002. Geophysical Research Abstracts, Vol. 5, 10286.

Besley, B M, and Cleal, C J. 1997. Upper Carboniferous stratigraphy of the West Midlands (U K) revised in the light of borehole geophysical logs and detrital compositional suites. Geological Journal, Vol. 32, 85–118.

Binney, E W. 1848. Sketch of the Drift Deposits of Manchester and its Neighbourhood. Memoir of the Manchester Literary and Philosophical Society, Vol. 8, 195–234.

Bowen, D Q, Phillips, F M, Mccabe, A M, Kuntz, P C, and Sykes, G A. 2002. New data for the Last Glacial Maximum in Great Britain and Ireland. Quaternary Science Reviews, Vol. 21, 89–101.

Brettle, M J. 2001. Sedimentology and high-resolution sequence stratigraphy of shallow water delta systems in the early Marsdenian (Namurian) Pennine Basin, northern England. Unpublished PhD thesis, University of Liverpool.

Bridge, D Mcc, Butcher, A, Hough, E, Kessler, H, Leliott, M, Price, S J, Reeves, H J, Tye, A M, Wildman, G, and Brown, S. 2010. Ground conditions in central Manchester and Salford: the use of the 3D geoscientific model as a basis for decision support in the built environment. British Geological Survey Research Report, RR/10/06.

Bristow, C S. 1988. Controls on sedimentation of the Rough Rock Group (Namurian) from the Pennine Basin of northern England. 114–131 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of North West Europe. Besley, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

British Standard 5930. 1999. Code of practice for site investigations. (London: British Standards Institution.)

Broadhurst, F M, and Simpson, I M. 1983. Syntectonic sedimentation, rigs, and fault reactivation in the Coal Measures of Britain. Journal of Geology, Vol. 91, 330–337.

Broadhurst, F M, and Simpson, I M. 2000. The Collyhurst Sandstone — a case of double identity. Proceedings of the Geologists' Association, Vol. 111, 83–85.

Calver, M A. 1968. Distribution of Westphalian marine faunas in Northern England and adjoining areas. Proceedings of the Yorkshire Geological Society, Vol. 37, l–72.

Chisholm, J I, Waters, C N, Hallsworth, C R, Turner, N, Strong, G E, and Jones, N S. 1996. Provenance of Lower Coal Measures around Bradford, West Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 51, l53–166.

Chiverrell, R C, Innes, J, Middleton, R, Plater, A J,and Thomas, G S P. 2004. Quaternary landscape evolution of the Isle of Man, Lancashire and south-west Cumbria. 5–38 in The Quaternary of the Isle of Man and north-west England: field guide. Chiverrell, R C, Plater, A, and Thomas, G S P (editors). (London : Quaternary Research Association.)

Cleal, C J, and Thomas, B A. 1996. British Upper Carboniferous Stratigraphy. Geological Conservation Review Series, No. 11, (London: Chapman and Hall.)

Collinson, J D. 1988. Controls on Namurian sedimentation in the Central Province basins of northern England. 85–101 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of North West Europe. Besley, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Collinson, J D, and Banks, N L. 1975. The Haslingden Flags (Namurian, G1) of south-east Lancashire: bar finger sands in the Pennine basin. Proceedings of the Yorkshire Geological Society, Vol. 40, 431–458.

Crofts, R G (editor). 2005a. Quaternary of the Rossendale Forest and Greater Manchester. Field Guide. (London: Quaternary Research Association.)

Crofts, R G. 2005b. Lake Rawtenstall and Stacksteads Gorge. 17–20 in Quaternary of the Rossendale Forest and Greater Manchester. Field Guide. Crofts, R G (editor). (London: Quaternary Research Association.)

Crofts, R G, and Humpage, A J. 2005. Tandle Hill. 26–28 in Quaternary of the Rossendale Forest and Greater Manchester. Field Guide. Crofts, R G. (editor). (London: Quaternary Research Association.)

Crofts, R G, Hough, E, and Northmore, K J. 2010. Geology of the Rochdale district — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey, Sheet 76 (England and Wales).

Culshaw, M G, and Crummy, J A. 1991. S W Essex — M25 Corridor: Engineering geology. British Geological Survey Technical Report, WN/90/2.

Davis, S R, and Wilkinson, D M. 2005. The environmental history of Astley Moss over the last 5000 years. 44–50 in Quaternary of the Rossendale Forest and Greater Manchester. Field Guide. Crofts, R G (editor). (London: Quaternary Research Association.)

Delaney, C. 2003. The Last Glacial Stage (the Devensian) in north-west England. North West Geographer, Vol. 3, 27–37.

Douglas, I. 1985. Geomorphology and urban development in the Manchester area. 337–352 in The geomorphology of north-west England. Johnson, R H (editor). (Manchester: Manchester University Press.)

Eager, R M C, and Broadhurst, F M (editors). 1991. Geology of the Manchester area. Geologists' Association Guide No. 7 (Second Edition). (London: Geologists' Association.)

Eagar, R M C, Baines, J G, Collinson, J D, Hardy, P G, Okolo, S A, and Pollard, J E. 1985. Trace fossil assemblages and their occurrence in Silesian (mid Carboniferous) deltaic sediments of the Central Pennine Basin, England. 99–149 in Biogenic Structures; their use in Interpreting Depositional Environments. Curran, H A (editor). Society of Economic Palaeontologists and Mineralogists Special Publication, No. 35.

Earp, J P, and Taylor, B J. 1986. Geology of country around Chester and Winsford. Memoir of the British Geological Survey, Sheet 109 (Englandand Wales).

Evans, D J, and Kirby, G A. 1999. The architecture of concealed Dinantian carbonate sequences over the Central Lancashire and Holme highs, northern England. Proceedings of the Yorkshire Geological Society, Vol. 52, 297–312.

Evans, D J, Walker, A S D, and Chadwick, R A. 2002. The Pennine Anticline, northern England— a continuing enigma? Proceedings of the Yorkshire Geological Society, Vol. 54, 17–34.

Gavagan, P. 2005. Theory as to possible local contributory cause of the Manchester earthquake swarm October/November 2002. Open University Geological Society Journal, Vol. 26, 23–24.

Glover, B W, Holloway, S, and Young, S R. 1993. An evaluation of coalbed methane potential in Great Britain. British Geological Survey Technical Report, WA/93/24.

Guion, P D, and Fielding, C R. 1988. Westphalian A and B sedimentation in the Pennine Basin, U K. 153–177 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of North West Europe. Besley, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Guion, P D, Fulton, I M, and Jones, N S. 1995. Sedimentary facies of the coal-bearing Westphalian A and B north of the Wales–Brabant High. 45–78 in European coal geology. Whateley, M K, and Spears, D A (editors). Special Publication of the Geological Society of London,No. 82.

Harrison, C, and Petch, J R. 1985. Ground movements in parts of Salford and Bury, Greater Manchester — aspects of urban geomorphology. 353–371 in The geomorphology of north-west England. Johnson, R H (editor). (Manchester: Manchester University press.)

Holdsworth, B K, and Collinson, J D. 1988. Millstone Grit cyclicity revisited. 132–152 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of North West Europe. Besley, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Hough, E, Kessler, H, Leliott, M, Price, S J, Reeves, H J, and Bridge, D Mcc. 2003. Look before you leap: the use of geoenvironmental data models for preliminary site appraisal. Proceedings of the seventh international conference of the International Affiliation of Land Reclamationists. Runcorn, United Kingdom, 13–16 May 2003.

Hull, E. 1864. Geology of the country around Oldham, including Manchester and its suburbs. Memoir of the Geological Survey of Great Britain. Quarter Sheets 88N W, 89N W and N E and 92S W. (London: HMSO.)

Hull, E, and Slater, J W. 1862. The geology of the country around Bolton-le-Moors (Old Series Sheet 89S E). Memoir (Sheet) of the Geological Survey of Britain (England and Wales). (London: HMSO.)

Humpage, A J. 2005. Pilsworth Quarry. 34–37 in Quaternary of the Rossendale Forest and Greater Manchester. Field Guide. Crofts, R G (editor). (London: Quaternary Research Association.)

Hunt, R. 1855. Mineral statistics of the United Kingdom of Great Britain and Ireland for 1853 and 1854. Memoirs of the Geological Survey (Mining Records). (London: HMSO.)

Jackson, I, Lowe, D J, Morigi, A N, and Mathers, S J. 1983. The sand and gravel resources of the country around Whitchurch and Malpas, Clywd, Cheshire. Institute of Geological Sciences Mineral Assessment Report, No. 136.

Johnson, R H. 1969. The glacial geomorphology of the area around Hyde, Cheshire. Proceedings of the Yorkshire Geological Society, Vol. 37, 189–230.

Johnson, R H. 1971. The last glaciation in North-west England: a general survey. Amateur Geologist, Vol. 5, 18–37.

Johnson, R H. 1985. The imprint of glaciation on the west Pennine uplands. 237–262 in The geomorphology of north-west England. Johnson, R H (editor). (Manchester: Manchester University Press.)

Jones, R C B. 1938. The stratigraphy of the Upper Coal Measures of South Lancashire. Summary of Progress of the Geological Survey of Great Britain, 1936. Part II, 1–19.

Jowett, A. 1914. The glacial geology of east Lancashire. Quarterly Journal of the Geological Society of London, Vol. 70, 199–231.

Kirby, G A, Baily, H E, Chadwick, R A, Evans, D J, Holliday, D W, Holloway, S, Hulbert, A G, Pharoah, T C, Smith, N J, Aitkenhead, N, and Birch, B. 2000. The structure and evolution of the Craven Basin and adjacent areas. Subsurface Memoir of the British Geological Survey.

Leeder, M R. 1982. Upper Palaeozoic basins of the British Isles — Caledonide inheritance verses plate margin processes. Journal of the Geological Society of London, Vol. 139, 479–491.

Longworth, D. 1985. The Quaternary history of the Lancashire Plain. 178–200 in The geomorphology of north-west England. Johnson, R H (editor). (Manchester: Manchester University Press.)

March, M C. 1918. The superficial deposits of Manchester. Memoir of the Manchester Literary and Philosophical Society, Vol. 62, 1–17.

Minchin, D J, Cameron, D G, Evans, D J, Lott, G K, Hobbs, S F, and Highley, D E. 2006. Mineral Resource Information in Support of National, Regional and Local Planning: Greater Manchester (Comprising Cities of Manchester and Salford and Metropolitan Boroughs of Bolton, Bury, Oldham, Rochdale, Stockport, Tameside, Trafford and Wigan). British Geological Survey Commissioned Report, C R/05/182N.

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Poole, E G, and Whiteman, A J. 1955. Variations in thickness of the Collyhurst Sandstone in theManchester area. Bulletin of the Geological Survey, No. 9, 33–41.

Poole, E G, and Whiteman, A J. 1961. The glacial drifts of the southern part of the Shropshire–Cheshire basin. Quarterly Journal of the Geological Society of London, Vol.117, 91–130.

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Thomas, G S P. 2005. North-east Wales. 41–58 in The glaciations of Wales and adjacent areas. Lewis, C A, and Richards, A (editors). (London: Logaston Press.)

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Waters, C N, Aitkenhead, N Jones, N S, and Chisholm, I J. 1996. Late Carboniferous stratigraphy and sedimentology of the Bradford area, and its implications for the regional geology of northern England. Proceedings of the Yorkshire Geological Society, Vol. 51, 87–101.

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Worsley, P. 1967. Problems in naming the Pleistocene deposits of the north-east Cheshire Plain. Mercian Geologist. Vol. 2, 159–161.

Worsley, P. 2005. The Cheshire –Shropshire Plain. 59–72 in The glaciations of Wales and adjacent areas. Lewis, C A, and Richards, A E (editors). (Hereford: Logaston Press.)

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Index to the 1:50 000 Series maps of the British Geological Survey

The map below shows the sheet boundaries and numbers of the 1:50 000 Series geological maps. The maps are numbered in three sequences, covering England and Wales, Northern Ireland, and Scotland. The west and east halves of most Scottish 1:50 000 maps are published separately. Almost all BGS maps are available flat or folded and cased.

(Index map)

The area described in this sheet explanation is indicated by a solid block.

British geological maps can be obtained from sales desks in the Survey's principal offices, through the BGS London Office at the Natural History Museum, and from BGS-approved stockists and agents.

Northern Ireland maps can be obtained from the Geological Survey of Northern Ireland.

Figures and plates

Figures

(Figure 1) Simplified bedrock geology map of the Manchester district.

(Figure 2) Principal early Carboniferous structures of the region.

(Figure 3) Stratigraphy from Heywood No. 1 Borehole geophysical log. Vertical scale is in metres (and feet) below kelly bushing of borehole.

(Figure 4) Namurian (Millstone Grit Group) and Westphalian (Coal Measures Group) sandstones of the Manchester district.

(Figure 5) Namurian and Westphalian coal seams of the Manchester district.

(Figure 6a) Pennine Lower Coal Measures Formation in the Manchester district.

(Figure 6b) Pennine Middle and Upper Coal Measures formations in the Manchester district.

(Figure 7) Glacial, periglacial and postglacial deposits of the Manchester district.

(Figure 8) Superficial deposits thickness map for the district. This extract from the May 2010 version of the BGS Superficial Deposits Thickness Model covers the Manchester district. It represents a mathematical interpolation made by creating a rockhead elevation model from the BGS borehole dataset and 1:50 000 scale digital map data. The surface was then subtracted from a digital terrain model (DTM) created by the NERC Centre for Ecology and Hydrology. The resulting derived grid of 50 x 50 m cells represents the thickness of material between the two surfaces, which includes both natural superficial deposits and made and infilled ground. Only boreholes that penetrated mapped artificial or superficial deposits with a drill length of greater than 5 m were utilised, and some of these have been excluded from the modelling for further reasons. The borehole data used to make the model are subject to a small degree of error, and data lodged with BGS since 2001 may not have been incorporated. Around 6600 boreholes within the district were used in modelling. The model provides indicative values of thickness and not definitive values. Where superficial deposits are known to occur, but there is no borehole data, the deposits are attributed a minimum thickness of 1.5 m. As a result, particularly in valley fill deposits (e.g., alluvium plus river terrace deposits), this can generate a chain of isolated thicker 'pods', separated by areas of minimum thickness, simulating superficial deposit-filled scour hollows where none are known to be present, as seen in (Figure 8) along the River Medlock south-east of Oldham. NB. The version of 1:50 000 scale digital map data used in the model is superseded by the survey data used to compile the 2011 editions of the geological maps. Therefore, the extent of natural superficial deposits and artificially modified ground differs between (Figure 8) and the 2011 editions of the geological map, for example, in the north-west.

(Figure 9) Principal mineral resources in the Manchester district.

(Figure 10) Engineering geological characteristics of the rocks and soils in the Manchester district. A general guide only to the engineering characteristics (British Standard 5930, 1999) of the deposits in the district is indicated below. In practice, ground conditions from site to site are further influenced by such factors as geological structure, topography, the presence of undermining, the presence of faults, the variable depths and degrees of weathering and human activity; such factors should also be considered prior to undertaking engineering development.

Plates

(Plate 1) Approximately 20 m of Pennine Lower Coal Measures Formation exposed at Lowside Brick Works SSSI, [SD 941 041]. The Blenfire Rock is exposed in the upper part of the quarry face, here as a channel-fill sand body that has been worked as a building stone. The Wigan Four Feet (Blenfire) Coal is preserved below, here a composite of three beds. A thin ripple laminated sandstone is present in the lower part of the quarry face, which overlies mudstone that was formerly worked for brick clay (P772118).

(Plate 2) Worsley Delf Rock (Pennine Upper Coal Measures Formation) at Worsley Canal Basin [SD 748 005]. Arched entrance to Worsley Coal Tunnel centre, bottom, which provided access to an extensive series of underground canals dug to work numerous coal seams including the Worsley Four Feet (P772403).

(Plate 3) Worsley Delf Rock (Pennine Upper Coal Measures Formation) at Collyhurst Quarry [SD 853 001]. Previously termed the 'Collyhurst Stone', this exposure shows about a metre of characteristic secondary reddened sandstone and thick beds that made it suitable for use as a building stone (P772120).

(Plate 4) Chester Pebble Beds Formation (Sherwood Sandstone Group) exposed in the backface of the disused Little Bolton Quarry, near Eccles [SJ 787 985]. The quarry was active during the late 1800s, and exposes up to 4 m of the middle part of the formation, which comprises mixed aeolian and fluvial sandstone facies (P772121).

(Plate 5) Pilsworth New Quarry, south face [SD 825 094]: contorted Pilsworth Moraine over undisturbed glaciofluvial sheet deposits, section approximately 5 m high (P772124).

(Plate 6) The River Medlock at Park Bridge [SD 947 002] in a deeply incised valley, cut in the late Devensian during fluvial rejuvenation, along part of which landslides have developed (P772119).

(Plate 7) Pin Mill Brow [SJ 856 978]. The dumping of cinders and other waste into the River Medlock caused a major flood in July 1872 (P772123).

(Front cover) Castlefield in central Manchester. The Chester Pebble Beds Formation (Sherwood Sandstone Group) are exposed along the Bridgewater Canal, with the Beetham Tower, built in 2007, a striking representative of redevelopment in the region (Photographer: P Witney; P770101).

(Rear cover)

(Geological succession) Summary of the geological succession of the district. Units not present at outcrop; proved in Heywood No. 1 Borehole (SD80NW/141) [SD 8385 0898]

(Index map) Index to the 1:50 000 Series maps of the British Geological Survey

Figures

(Figure 4) Namurian (Millstone Grit Group) and Westphalian (Coal Measures Group) sandstones of the Manchester district

Unit (former name(s)) Map code Thickness (m) Lithology
Pennine Upper Coal Measures Formation
Openshaw Sandstone OpS 0–15 Sandstone, fine to medium grained, well bedded
Worsley Delf Rock WDR 0–15 Sandstone, fine to medium grained, well bedded
Pennine Middle Coal Measures Formation
Newton Heath Sandstone NHS 15–20 Sandstone, fine to medium grained, well bedded
Nob End Rock NR 0–30 Sandstone, fine to medium grained, well bedded
Pemberton Rock (Bardsley, Peel Hall) PR 0–55 Sandstone, fine to medium grained, well bedded
Huncliffe Rock (Foxholes) HR 0–40 Sandstone, fine to medium grained, well bedded
Pennine Lower Coal Measures Formation (*not shown on map face)
Chamber Rock ChR 15–60 Sandstone, fine to medium grained, well bedded
Blenfire Rock BR 0–50 Sandstone, fine to medium grained, well bedded
Trencherbone Rock TR 0–15 Sandstone, grey-brown, fine grained, cross-bedded, with ironstone concretions and numerous mudstone interbeds
Cannel Rock CaR 0–55 Sandstone, fine grained, medium bedded, cross-bedded or massive
Royley Sandstone Ro 0–15 Sandstone, medium grained, medium bedded, cross-bedded
Old Lawrence Rock OL 15–55 Sandstone, greenish grey, fine to medium grained, parallel-bedded and ripple-laminated, with subordinate mudstone interbeds
Milnrow Sandstone (Crutchman Sandstone) MS 5–12 Sandstone, weathers ochreous, mainly medium grained, cross-bedded or massive
Darwen Flags (Trough Edge End Sandstone) DF 0–10 Sandstone, fine grained, ripple laminated, micaceous
Icconhurst Sandstone* IS 0–15 Sandstone, grey and brown, cross-bedded
Helpet Edge Rock (Warmden Sandstone) HE 17–30 Sandstone, grey-brown, fine to coarse grained, large scale cross-bedded or massive
Inch Rock* IR 0–about 5 Sandstone, fine to medium grained, yellow and brown
Great Arc Sandstone (Bullion Rock) GA 0–5 Sandstone, fine to medium grained, cross-bedded and ripple laminated
Gannister Rock* GR 0–15 Sandstone, medium grained, cross-bedded and ripple laminated; siliceous in upper part
Lower Foot Rock* LFR 0–2 Sandstone, fine grained, ripple laminated, micaceous
Woodhead Hill Rock WHR 10–25 Sandstone, weathers ochreous, mainly medium grained with rare pebbles, thickly cross-bedded in upper part, parallel bedded in lower part
Ousel Nest Grit ON 0–30 Sandstone, medium to coarse grained, thickly bedded, cross-bedded
Margery Flags MF 0–5 Sandstone, fine grained, thinly bedded, ripple laminated, micaceous
Named sandstones present at outcrop within the Millstone Grit Group
Rough Rock RR 15–30 Sandstone, grey, weathering ochreous, medium to very coarse grained, with quartz pebbles, poorly sorted, thickly cross-bedded
Rough Rock Flags RF 3–10 Sandstone, grey-brown, very fine to fine grained, ripple laminated, micaceous
Upper Haslingden Flags UH 0–15 Sandstone, greenish grey, very fine to fine grained, thinly bedded, ripple laminated, interbedded with sandy siltstone
Lower Haslingden Flags LH 0–60 Sandstone, greenish grey, very fine to fine grained, thinly bedded, ripple laminated, interbedded with sandy siltstone
Holcombe Brook Grit HB 0–17 Sandstone, medium grained, thickly bedded, cross-bedded, well sorted
Huddersfield White Rock WR 0–10 Sandstone, fine to medium grained, thinly bedded, ripple laminated
Brooksbottoms Grit BB 0–12 Sandstone, fine to medium grained, thinly bedded, ripple-laminated
Guiseley (Hazel Greave) Grit G 0–35 Sandstone, fine to medium grained, cross-bedded and cross-stratified, ganister at top
Helmshore Grit HG 0–10 Sandstone, medium to coarse grained, thickly bedded, cross-bedded
Fletcher Bank Grit (Gorpley Grit) FB 15–50 Sandstone, medium to coarse grained, thickly bedded, cross-bedded
East Carlton Grit/Readycon Dean Flags EC 15–50 Sandstone, medium to coarse grained, thickly bedded, cross-bedded

(Figure 5) Namurian and Westphalian coal seams of the Manchester district

Coal seam (alternative name(s)) Map code Thickness (m) Type of workings
Pennine Upper Coal Measures Formation
Openshaw Op 0.1
Charlotte Ct 0.3
Bradford Three quarters Br3Q 0.3 Deep mined
Bradford Four Foot Coal Br4 0.6 Deep mined
Slack Lane (Two Feet) SL 0.3 Not worked
Pennine Middle Coal Measures Formation
Worsley Four Feet W4 0.2–1.3 Deep mined
Parker Pr 0.5–0.9 Deep mined
Radley Ra 0.2 Not worked
Cannel Can 0.2 Not worked
New Jet Amber NJA 0.6 Deep mined
Riding Rd 0.8 Not worked
Park (Pottery) Pk 0.4–1.4 Deep mined
Park Yard (Ashclough) PY 0.0–0.3 Not worked
Ince New (Major, Stonedelph) IN 0.8–1.1 Deep mined
Ince Yard (Bland, Bin, Binn) IY 0.6–1.3 Deep mined and surface mined (opencast)
Crumbouke (Colonel) Cb 0.8–1.5 Deep mined and surface mined (opencast)
Ashton Great AG 0.0–2.2 Deep mined
Brassey (Roger) BR 0.3–1.2 Deep mined
Top Furnace TF 0.2–0.7 Deep mined
Rams Coal (Bottom Furnace) Rams 0.8–2.4 Deep mined and surface mined (opencast)
Stubbs St 0.0–0.4 Not worked
Fairbottom (Bargan) F 0.3–0.7 Deep mined and surface mined (opencast)
Pemberton Five Foot (Hard, Windmill, Higher Florida) P5 0.4–0.8 Deep mined and surface mined (opencast)
Park (Lower Yard) Pk 0.1–0.8 Deep mined
White (Foxholes, Lower Florida) WH 0.3–1.5 Deep mined and surface mined (opencast)
Pemberton Two Foot (Cannel, Two Feet) P2 0.0–0.8 Not worked
Pemberton Four Foot (Black, Town Lane) P4 0.0–1.3 Not worked
Top Shuttles (Gigham) TSh 0.0–0.1 Not worked
Pennine Lower Coal Measures Formation
Doe (Hathershaw, Bottom Shuttles) Ha 0.0–0.2 Not worked
Higher Chamber (Bancroft) HCh 0.0–0.3
Lower Chamber (Little) LCh 0.0–0.4 Not worked
Wigan Five Feet Wg5 0.1–0.6 Deep mined
Wigan Four Feet (Foggs, Five Quarters) Wg4 0.1–1.3 Deep mined and surface mined (opencast)
Wigan Two Feet (Blenfire, Lower Victoria) Wg2 0.1–0.6 Deep mined
Trencherbone (Wigan Six Feet, Oldham Great) T 2.0–4.8 Deep mined; surface mined (opencast)
Peacock (Saltpetre, Cellar) Pe 0.5–1.8 Not worked
Smithy Sy 0.0–0.2 Not worked
Little Black (Little, Little King) LB 0.1–0.6 Surface mined (opencast)
Cannel (Black) CAN 0.3–0.9 Deep mined and surface mined (opencast)
King K 0.0–1.3 Deep mined and surface mined (opencast)
Queen (Foot, Sapling) Q 0.6–1.5 Deep mined
Ravine (Stone, Plodder) RAV 0.9–2.5 Deep mined
Higher Bent HBt 0.0–0.5 Not worked
Lower Bent LBt 0.3–0.9 Deep mined
Foot Ft 0.0–0.2 Not worked
Nayley Na 0.0–0.8 Not worked
Davis Da 0.0–0.5 Not worked
Seddon Se 0.4 Not worked
Water Wa 0.0–0.2 Not worked
Olive O 0.0–0.5 Not worked
Yard Tops (Higher Two) YT 0.0–0.8 Deep mined and crop working
Yard Bottoms (Old, Lower Two) YB 0.6–2.5 Deep mined and crop working
Yard Y 0.0–0.8 Deep mined
Half Yard (Top Neddy, New) HY 0.6–1.2 Deep mined
Three Quarters (Cockloft) 3Q 0.2–0.9 Deep mined
Smith (Bottom Neddy, Three Quarters) Sm 0.0–1.7 Deep mined and crop working
Arley A 0.9–2.0 Deep mined, crop working and surface mined (opencast)
Dib Hole DH 0.0–0.1 Not worked
Pasture P 0.1–1.2 Crop working
Cemetery Cm 0.0–0.4 Crop working
Union U 0.8–1.6 Deep mined and crop working
Cannel Ca 0.0–0.9 Deep mined and crop working
Upper Mountain UM 0.0–1.1 Deep mined and crop working
Inch I 0.0–0.5 Deep mined and crop working
Upper Foot (Bullion) UF 0.0–0.7 Deep mined and crop working
Lower Mountain LM 0.0–1.3 Deep mined and crop working
Lower Foot LF 0.0–0.8 Deep mined and crop working
Bassy B 0.0–1.2 Deep mined and crop working
Margery M 0.0–0.2 Not worked
Coals within the Millstone Grit Group
Sand Rock Coal SR 0–0.7 Deep mined and crop worked
Holcombe Brook Coal HBC 0–0.4 Crop worked

(Figure 7) Glacial, periglacial and postglacial deposits of the Manchester district

Type Thickness (m) Morphology Deposit
Head (periglacial solifluction deposits) Locally common; generally less than 5 Accumulations in hollows, shallow valleys and at the base of slopes Poorly consolidated and unsorted deposits, composition closely reflects the upslope source material, varies considerably from sandy clay to clayey sand; shear surfaces may be common
Peat Locally exceeds 3 Extensive areas of raised mires; flat spreads in hollows and on high moorland Organic soil
Alluvium Up to 3 Narrow flats in channels and tributaries of the rivers Irwell and Roch Heterogeneous clay, silt and sand with rare gravel lags and peat lenses
Alluvial fan deposits Up to 5 Fans at confluence of side valleys with main valleys Silt, sand and gravel
River terrace deposits (1–3, or undifferentiated) Up to 3 Flat surfaces above alluvium in the Irwell valley Silt, sand and gravel
Lacustrine deposits Highly variable, 3–10 Accumulations in hollows Poorly consolidated, soft, clay and silt, commonly laminated
Glaciofluvial deposits, undifferentiated Highly variable, estimated up to 5 Featureless accumulations of sand and gravel Mainly bedded sand and rare gravel; may be clayey in part
Glaciofluvial sheet deposits (1–3, or undifferentiated) Highly variable, but up to 30 Sheet-like spreads; either concealed beneath till or occurring as valley trains Mainly bedded sand and rare gravel; may be clayey in part
Glaciofluvial subaqueous fan deposits Highly variable, but up to 5 Flat spreads Mainly bedded sand and rare gravel and impersistent beds of silt
Ice-contact deposits Highly variable, but up to 10 Low mounds or interbedded in till; laterally impersistent Mainly bedded sand and rare gravel and impersistent beds of clay
Glaciolacustrine deposits Highly variable, but up to 20 Flat spreads Poorly consolidated, soft, laminated clay and silt
Glaciolacustrine deltaic deposits Up to 10 Flat spreads Sand and gravel, cross-bedded
Morainic deposits Highly variable, but up to 40 Irregular mounds and ridges, commonly with steep ice-contact slope Very variable including stony clays, silt, laminated clay, sand and gravel
Till Highly variable, locally up to 35 Featureless spreads Kettle kame topography Lodgement till; very stiff, overconsolidated grey-brown or red-brown clay matrix with varying proportions of sand, silt and pebbles. It also contains cobbles, and more rarely boulders Ablation till; normally consolidated, unsorted grey-brown sandy silty clay

(Figure 9) Principal mineral resources in the Manchester district

Mineral resource Source Activity Use
Sand and gravel Glaciofluvial deposits, alluvium and river terrace deposits, weathered Chester Pebble Beds Formation bedrock Glaciofluvial deposits currently worked east of Bury, and Town Lane Concrete aggregate; building and asphalt sand
Crushed rock aggregate (most Namurian and Westphalian, and some Permo-Triassic sandstones have been worked; those widely exploited are listed, right) Chester Pebble Beds Formation; Pennine Upper Coal Measures Formation (Worsley Delf Rock); Pennine Lower Coal Measures Formation (Old Lawrence Rock, Milnrow Sandstone, Woodhead Hill Grit, Ousel Nest Grit) Old Lawrence Rock (Pennine Lower Coal Measures Formation) currently worked at Harwood, north of Bolton Constructional fill
Building stone Carboniferous and Permo-Triassic sandstones Currently no workings Building and walling stone; repairs to existing buildings
Limestone Halesowen and Manchester Marls formations Formerly deep mined in the Beswick and Blackmoor areas; no current workings Constituent of cement
Brick clay Coal Measures Group Till Formerly of great importance; one licensed pit currently active at Harwood working the Pennine Lower Coal Measures Formation Facing, engineering and paving bricks
Peat Upland and lowland peat Formerly of minor importance; currently three sites at Chat Moss active Domestic fuel; unsuitable for horticultural purposes
Coal Coal Measures Group, Millstone Grit Group Formerly of great importance; no deep mines active; one surface mine (opencast) site licensed at Greenheys (Cutacre site), working coal seams from the Pennine Middle Coal Measures Formation Engine, household, gas and coking coals
Coalbed methane Coal Measures Group Potential; currently exploited to the south-west of the district Natural gas
Oil and gas (conventional) Carboniferous sandstones Probably insignificant Oil and gas
Shale gas Namurian and Visean mudstone Currently being explored to the north-west of the district; potential unknown Natural gas
Made ground Sandstone spoil, Mine stone (burnt shale) Little utilised Bulk-fill

(Figure 10) Engineering geological characteristics of the rocks and soils in the Manchester district

Engineering geological units Geological units Description/ characteristics Engineering considerations
Engineering soils Foundations Excavation Engineering fill Site investigation
Highly variable artificial deposits Made ground Highly variable composition, thickness and geotechnical properties Highly variable. May be unevenly and highly compressible. Hazardous waste may be present causing leachate and methane production Usually diggable. Hazardous waste may be present at some sites Highly variable. Some material may be suitable Essential to determine depth, extent, condition and type of fill. Care needs to be taken as presence of pollution and contaminated ground likely. Essential to best practice.
Coarse soils Head

Alluvium (sand and gravel dominated; basal gravel lags)

Alluvial fan deposits

River terrace deposits

Glaciofluvial and ice-contact deposits

 Medium dense to dense SAND & GRAVEL with some buried channels and lenses of clay, silt & peat Generally good. Variable thickness of deposit. Thick deposits in buried channels may be significant in foundation design due to differential settlement Diggable. Support may be required. May be water bearing Suitable as granular fill Important to identify the presence and dimension of buried channels and characteristic of infilling deposits. Geophysical methods may be applicable
Glaciolacustrine deltaic deposits (sand and gravel) Loose to medium dense fine to medium SAND Poor foundation Easily diggable. Generally poor stability. Running sand conditions possible below the water table and in pockets at perched water tables Unsuitable as granular fill Determine the presence, depth and extent of deposit and depth to sound strata
Fine soils Firm Till

Morainic deposits

 Firm to very stiff sandy, gravelly CLAY with some channels and lenses of medium dense to dense sand and gravel Generally good foundation, although sand lenses may cause differential settlement. Possibility of pre-existing slips can also cause a strength reduction Diggable. Support may be required if sand lenses or pre-existing slips encountered. Ponding of water may cause problems when working Generally suitable if care taken in selection and extraction. Moisture content must be suitable Determine the depth and extent of deposit, especially the frequency and extent of lenses and channels. Investigate whether any pre-existing slips and shear planes are present
Soft Alluvium (silt and clay dominated; abandoned channel deposits) Soft to firm CLAY some sand, gravel and peat lenses Poor foundation. Soft highly compressible zones may be present; risk of differential settlement Easily diggable. Moderate stability, decreasing with increasing moisture content. Running sand conditions possible below the water table and in pockets with perched water tables. Risk of flooding Generally unsuitable Determine the presence, depth and extent of soft compressible zones and depth to sound strata
Lacustrine deposits

Glaciolacustrine deltaic deposits (clay and silt)

 Soft to stiff laminated CLAY with some lenses of sand Generally poor foundation as long-term consolidation and differential settlement possible Easily diggable. Support may be required if sand lenses encountered in deep excavations. Ponding of water or exposure to rain may cause softening of formation Generally suitable if care taken in selection and extraction. Moisture content must be suitable Determine the depth and extent of deposit, especially the frequency and extent of lenses
Organic soils Peat Very soft to soft brown fibrous or amorphous PEAT Very poor; very weak; highly compressible foundation. Acidic groundwater Diggable. Poor stability. Generally wet ground conditions Generally unsuitable Determine the depth and extent of deposit and groundwater's acidity
Engineering rocks
Weak sandstone Sherwood Sandstone Group

Appleby Group

 Moderately weak to moderately strong yellow, reddish brown fine- to medium-grained poorly to very well sorted; poorly cemented SANDSTONE occasionally gravelly. Weathers to medium dense to very dense sand up to depths of 5m Generally good provided suitable design is adopted and the depth of weathered rockhead is determined Dependent on discontinuity spacing and degree of weathering. Ripping or pneumatic tools or blasting generally required Suitable as high grade fill, if care taken in selection and extraction Essential to determine depth and properties of weathered zone. In situ loading tests advisable to assess weak sandstone bearing strengths at selected sites
Strong sandstone Sandstone units of the Pennine Coal Measures Group

Millstone Grit Group

 Moderately weak to strong dark grey to grey laminated MUDSTONE, SILTSTONE and SHALE. Weathers to a firm to stiff brown and grey clay Generally good provided suitable design is adopted. Possibility of strength variability due to fissuring and weathering. Presence of highly weathered zones needs to be assessed Diggable where rocks are weathered. Ripping or pneumatic tools maybe required at depth in fresh rock Suitable for under controlled compaction conditions. Moisture content must be suitable general fill Essential to determine depth and extent of strata, the discontinuity spacing and weathering
Weak mudstone Cumbrian Coast Group Stiff to weak, reddish brown or purple MUDSTONE. Weathers to a soft to stiff clay Generally good provided suitable design is adopted. Possibility of strength variability due to fissuring and weathering. Presence of highly weathered zones needs to be assessed Diggable where rocks are weathered. Ripping or pneumatic tools maybe required at depth in fresh rock Suitable for general fill under controlled compaction conditions. Moisture content must be suitable Essential to determine depth and extent of strata, discontinuity spacing and weathering
Strong mudstone Mudstone units of the Pennine Lower and Middle Coal Measures formations

Millstone Grit Group

 Moderately weak to strong dark grey to grey laminated MUDSTONE, SILTSTONE and SHALE. Weathers to a firm to stiff brown and grey clay Generally good provided suitable design is adopted. Possibility of strength variability due to fissuring and weathering. Presence of highly weathered zones needs to be assessed Diggable where rocks are weathered. Ripping or pneumatic tools maybe required at depth Suitable for general fill under controlled compaction conditions. Moisture content must be suitable Essential to determine depth and extent of strata, the extent of discontinuity spacing and weathering
Interbedded mudstone, siltstone & sandstone Warwickshire Group; Pennine Upper Coal Measures Formation Weak to moderately strong grey interbedded MUDSTONE, SILTSTONE and fine to coarse grained SANDSTONE. Mudstone and siltstone weathers to a very soft to stiff clay Generally good provided suitable design is adopted and the depth of weathered rock head is determined. Locally high sulphate conditions Weathered mudstones usually diggable. Ripping or pneumatic tools required at depth in fresh rock Suitable for general fill under controlled compaction conditions. Moisture content must be suitable Essential to determine depth and properties of weathered zone. In situ loading tests advisable to assess bearing strengths at selected sites
Limestone Limestone units within the Warwickshire Group (including GREAT MINE LIMESTONE) Strong to very strong, dark grey to light grey LIMESTONE with some mudstone interbeds Generally good provided suitable design is adopted. Bed thickness needs to be assessed Dependent on discontinuity spacing and mudstone interbeds. Ripping or pneumatic tools or blasting generally required Suitable as high grade fill, if care taken in selection and extraction Important to identify the presence of locally highly weathered zones and natural cavities. In situ loading tests advisable to assess bearing strengths at selected sites